Email Warmup: What It Is, How It Works, and How Long It Takes

Since January 2026 we’ve sent 116,369,926 warmup emails from 221,644 mailboxes connected to TrulyInbox, across 46,044 workspaces.

So we know a thing or two about warmup and how warmup works. Every placement figure below is filtered to paying accounts.

TL;DR

• Warmup builds sender reputation before you need it. Providers let your early mail through so they can watch what you do with it. Warmup makes sure what they see is good.
• Give it three to four weeks. On a new account and a new domain, that’s the number. A domain with damaged reputation needs four to six.
• A good day-one score is not a green light. New accounts often start high because providers are still evaluating you. That number falls once you start sending for real.
• Microsoft is the strict one. Across our paid accounts, Google Workspace places 91.5% and Microsoft 365 places 79.0%.
• Authentication does not show its value until week two. In our own test, accounts missing records looked fine for ten days and then dropped to the 70–80% range and stayed there.
• Warmup never stops. It builds reputation before outreach, holds it during, and repairs it after.

What Is Email Warmup?

Email warmup is the process of gradually sending and receiving mail from a new or inactive mailbox. It runs before real outreach, so providers can build a positive sender reputation first.

Warmup replaces an empty sending history with evidence of genuine engagement: opens, replies, and messages rescued from spam.

That evidence is what the filter reads.

The part most guides get wrong:

• Providers don’t slam the door on a new mailbox. The filters don’t act immediately at all, they let you send a few emails first and watch what happens.
• Your first messages generally do land in the inbox, precisely so the algorithm has something to evaluate. You only get filtered on day one if those first emails already look like a spammer or a phisher.

That’s why warmup works.

You get a short window where you’re being assessed, and warmup fills it with good behaviour instead of cold outreach. Waste that window and you spend months earning it back.

What Email Warmup Is Not?

Warmup isn’t a deliverability fix, it builds reputation where none exists, and that’s the whole of what it does.

If your authentication is broken, your domain is blacklisted, or your list is scraped, warmup won’t save you. You’ll just reach those problems faster, with a healthier-looking sender profile attached.

It also isn’t a substitute for patience, and nobody has found a way to compress three weeks of observed behaviour into three days.

What Is Warming Up an Inbox?

Same thing, different phrasing. “Warming up an inbox” points at the mailbox rather than the domain behind it.

That distinction matters once you’re running several mailboxes on one domain, because each mailbox earns its own reputation while also feeding the domain’s.

How Does Email Warmup Work?

The mechanics are simpler than the marketing around them suggests.

• Your mailbox joins a pool of real, active mailboxes
• It sends a small number of messages each day to others in that pool
• Those recipients open them, reply, and pull anything that landed in spam back out
• Volume climbs on a schedule, not all at once
• Providers watch the pattern and form a view of you

The reply is the signal that carries the most weight. It’s expensive to fake. And it tells the provider the mail was wanted rather than merely delivered.

What Actually Happens During Warmup?

Providers are running a scoring model, and warmup feeds it.

Nobody outside Google and Microsoft knows what’s in that model. There are thousands of signals and the weighting isn’t published.

Anyone who tells you they know how the filter works is guessing. That includes us.

What we do have is a decade of collective experimentation, our own testing, and what deliverability people compare notes on. That’s the basis for everything in this guide, and I’d rather say so than pretend otherwise.

How Warmup Simulates Human Engagement?

Real engagement means a message opened after a plausible delay, read, and answered in the thread. Fake engagement means a bot opening 400 messages in eight seconds from one data centre.

Aim for a high reply rate in your warmup pool, because it does two jobs.

• First, replies are the strongest positive signal you can generate. They build reputation faster than opens ever will.
• Second, once cold outreach starts, most of that mail gets no reply at all. A strong warmup reply rate keeps the account’s overall engagement up. 

Email Warmup vs Domain Warmup vs SMTP and IP Warmup

These are four names for the same activity. What differs is where the reputation attaches, not what you actually do.

• Email warmup builds reputation for one mailbox, and that is the base case everything else sits on.
• Domain warmup is what happens when you warm all the mailboxes on a domain, because domains carry reputation the same way mailboxes do.
• IP warmup matters depending on how you send. On Google Workspace or Microsoft 365 you’re on a shared IP you don’t control.

Some providers offer private IPs, and the good ones hold well-reputed address space while rotating IPs so you don’t inherit a blacklisting.

Even then, warming your mailboxes builds that IP reputation too. It’s all connected.

SMTP warmup needs saying plainly:

You cannot warm up SMTP. It’s a protocol. What people mean is warming up the mailboxes that send over SMTP, which is the same thing again.

Term	What the reputation attaches to	Who it applies to
Email warmup	One mailbox	Everyone
Domain warmup	The domain, built by warming its mailboxes	Anyone launching a new outreach domain
IP warmup	The sending IP	Mostly relevant on private or dedicated IPs
SMTP warmup	Nothing extra. It means warming SMTP-connected mailboxes	Senders on a relay rather than a mailbox provider

Why Email Warmup Matters More in 2026?

The bar moved twice in two years, and both times it moved the same way.

Gmail and Yahoo, February 2024

Bulk senders pushing 5,000+ messages a day to Gmail got hard requirements. SPF, DKIM and DMARC became mandatory, as did one-click unsubscribe.

Spam complaints got a number attached too: stay under 0.3%, and ideally under 0.1%.

Microsoft, 2024 to 2025

Microsoft tightened along the same lines, bringing authentication enforcement to high-volume senders aimed at Outlook and Hotmail domains.

Microsoft has always been the harder one to read. It publishes far less than Google, and its junk folder is stickier once you land there.

Yahoo and AOL, October 2024

Yahoo followed with its own enforcement, and DMARC alignment stopped being optional.

This one matters less for B2B outreach than the headlines suggested, because Yahoo and AOL are consumer mailboxes. Worth knowing, rarely worth planning around.

What This Means for Warmup in 2026?

Authentication is table stakes now rather than an advantage, because everyone competent has it and the providers assume it.

What separates senders is behaviour over time, which is exactly what warmup produces.

How Inbox Providers Evaluate Senders?

There are a great many factors, and nobody outside the providers knows all of them or how they’re weighted. Treat every published list, including this one, as informed inference. Ours included.

What we can say is which behaviours consistently move the needle in testing.

The 4 Reputation Layers

• Domain reputation — tied to your DKIM signing domain
• IP reputation — tied to the sending IP, shared on Google Workspace and Microsoft 365
• Content reputation — patterns in your body copy, links and attachments
• URL reputation — your tracking domain, and every link inside the email

Most people optimise the first and forget the last. That’s why tracking domains are such a quiet killer, and why almost nobody checks theirs.

Signals That Matter Most, Ranked by Weight

This ranking comes from our own testing and from what the wider deliverability community consistently observes. It is not published by any provider.

Signal	Direction	Weight	Why
Reply	Positive	Strongest	A reply tells the provider the mail was wanted
Spam rescue (moved out of junk)	Positive	Strong	A direct override of the filter’s own decision
Open, with time-to-read	Positive	Moderate	Opens alone carry less weight than opens plus dwell
Mark as important or star	Positive	Moderate	Explicit user intent
Spam complaint	Negative	Strongest negative	Even 0.1% on a new account triggers scrutiny
Bounce	Negative	Strong	A proxy for list quality. Above 2% is a red flag
Delete without opening	Negative	Weak	Meaningful only in volume

How to Monitor Your Sender Reputation?

Both of the free monitoring tools changed recently, and most guides still describe the old versions.

• Google Postmaster Tools –  Version 1 was retired on 30 September 2025 and switched off after 31 October. Version 2 is now the only one. The Domain and IP Reputation dashboards are gone.

Google removed them on the basis that a single reputation score misled people when it’s one input among many. In their place is a Compliance dashboard, which gives you a straight pass or fail against the sender guidelines.

Which gives you a quick way to date any advice you read:

• If a guide tells you to watch your domain reputation trend weekly, it was written before October 2025.
• What you check now is compliance status, spam complaint rate, and authentication results.

Microsoft SNDS is still running, and still only useful if you control your sending IP, which most cold senders don’t.

It moved to a new portal on 8 June 2026, and the old automated-access URLs were deprecated on 22 June.

IP Status and IP Data now come from a REST API with OAuth 2.0. Automated CSV links expire after 30 days.

The related complaint feed, JMRP, now delivers in standard ARF format. The sender address is redacted and the message body removed, and spam-trap hit data has been withdrawn.

If your JMRP feed isn’t linked to an SNDS account with current network access, it was dropped in the migration.

What to Set Up Before You Start Warmup?

Warmup on a broken setup is wasted time. An hour here saves you a fortnight later.

Dedicated Outreach Domain

Do this first, before anything else:

• Never run cold outreach from your primary domain.
• One bad campaign should not put your invoices and your customer replies in spam.
• Register a close variant of your brand, point it at your main site, and buy it at least a month before you need it. Domains are cheap. Recovering a burned one is not.
• New domains carry a filtering penalty for roughly their first month, and that clock starts at registration rather than at first send.
• Keep it to three or four mailboxes per domain, because more than that on a fresh domain looks like exactly what it is.

SPF, DKIM and DMARC

Setup SPF, DKIM and DMARC before your first warmup send.

• SPF lists who may send for your domain. DKIM signs the message so it can be verified. DMARC tells providers what to do when those two disagree.
• Start DMARC on p=none and read the reports for a fortnight. Move to quarantine once nothing legitimate is failing.

Here’s the trap:

You can get away without them for a while. That’s exactly what makes them dangerous.

So we tested it – We ran 20 new mailboxes across 5 domains, varying the authentication stack per group.

The groups were – SPF only, SPF and DKIM without DMARC, DKIM and DMARC without SPF, nothing at all, and the full set. 

It got worse when real outreach started.

Running warmup and cold outreach at a 1:1 ratio, placement fell to under 45–50% across those accounts, because overall positive interaction dropped. Raising the ratio to 2:1 warmup to outreach brought it back to 58–62%.

That 2:1 figure is where our recommendation comes from.

We still can’t tell you why some of those messages got through and others didn’t.

What we can say is that enterprises themselves reject mail from senders without these records. And that Microsoft pushes hardest on missing authentication, which showed up clearly in placement testing.

Infrastructure Readiness

• MX records: A domain that can’t receive mail looks like a domain built to send and vanish, and providers notice.
• DNS hygiene: Check that your records resolve cleanly, that there aren’t two conflicting SPF records, and that your DKIM selector actually publishes a key.

Broken records are more common than missing ones.

Inbox Setup

• Fill in the profile: Name, photo, signature. An empty mailbox with no display name is a pattern providers already associate with throwaway senders. It costs five minutes.

Custom Tracking Domain

• Shared tracking domains inherit the reputation of everyone else using them, and that includes the worst sender on the platform.
• Set up your own subdomain instead. It takes ten minutes, and it closes a risk you can’t otherwise control.

How to Warm Up an Email Account? The Ramp Schedule

Phase 1 to Phase 4, Day by Day

Warmup has four phases, and the boundaries between them are gates rather than dates.

1. Establish (days 1–7) — tiny volume, zero bounces
2. Build (days 8–21) — volume climbs steadily while engagement holds
3. Prove (days 22–28) — hold at target and confirm placement with a real test
4. Run alongside (day 29+) — cold outreach starts, warmup keeps going underneath it

The Day-by-Day Warmup Schedule

The target is 50 warmup sends a day by the end of week four. Increase by a fixed number of messages, never by a percentage, because percentages compound into exactly the spike that gets you filtered.

Day range	Warmup volume	Cold outreach	Reply rate target	Gate to clear
Days 1 to 3	5/day	0	20%+	Bounce rate 0%
Days 4 to 7	10/day	0	20%+	No spam placement
Days 8 to 14	20/day	0	20%+	0 complaints
Days 15 to 21	35/day	0	20%+	Placement climbing
Days 22 to 28	50/day	0	20%+	Inbox placement test passed
Day 29+	50 to 60/day	Start at 10 to 15/day	40%+	Warmup at 2:1 against outreach

The gate column is the real instruction. Day ranges describe a typical account, gates describe yours, and where they disagree the gates win.

Note the ceiling. 50 to 60 warmup emails a day is enough, and there’s no benefit to pushing past it.

Schedule Your Warm Up Emails

If your warmup tool lets you schedule sends, schedule them the way you’d actually send.

I run mine 9am to 12pm and 2pm to 5pm, with randomised gaps rather than fixed intervals. A mailbox that fires eight messages in ninety seconds at 09:00 every morning is describing itself accurately to the filter.

Personally I don’t warm up on Saturdays or Sundays. That’s a preference rather than a rule, but it costs nothing and it looks more like a working mailbox.

How Fast Can You Safely Ramp New Inboxes?

Slower than you want to: three to four weeks to reach 50 sends a day is the right pace.

Work backwards and the increments are small.

5 a day for the first three days. 10 by the end of week one, 20 by the end of week two. Then 35 by the end of week three, and 50 by day 28.

That’s an average of under two extra messages a day.

If a day goes badly, hold. Don’t drop back to zero. Don’t push through it either.

Email Warmup Best Practices for 2026

• Warm every mailbox before it sends anything cold, including replacements
• Keep warmup running after outreach starts, at a 2:1 ratio against cold volume
• Cap warmup at 50 to 60 sends a day
• Fix authentication first, because warmup can’t compensate for it
• Run an inbox placement test at week four rather than trusting a dashboard score

How Long Does Email Warmup Take?

Three to four weeks on a new account and a new domain. Four to six weeks if the domain carries damaged reputation.

Here’s what that looks like in our data, filtered to paying accounts. 

That week-one figure is worth sitting with, because it explains the single most common mistake we see.

New accounts often start high, because providers are still evaluating you and early mail gets through.

Depending on the account, the domain and their age, people see anywhere from 70% to 90% on day one. Old accounts, long-dormant accounts and anything with prior reputation damage sit below 80%.

A good starting score is not permission to start sending.

We get this support conversation regularly. The dashboard says 90%, they launch outreach, and their mail lands in spam.

Asked how long they warmed for, the answer is usually a week, maybe a week and a half. And they went straight to 50 cold emails a day.

What happens next is that they buy a fresh set of domains and start over, or they decide cold email is dead. Neither was the problem. The warmup period was.

Warmup Timelines by Provider

Every business provider lands in the same three-to-four-week range. What differs is where you end up, not how long it takes to get there. That surprises people.

Provider	Typical time to stable placement	Our measured placement	What to watch
Google Workspace	3 to 4 weeks	91.5%	Compliance status in Postmaster Tools v2, and the Promotions tab
Microsoft 365	3 to 4 weeks	79.0%	421 deferrals in week one, which are normal rate limiting
Zoho, Amazon SES and others	3 to 4 weeks	85.9%	Authentication alignment and bounce rate

Microsoft is the strict one, and the gap is not small. Its filters are tighter than Google’s across the board.

Once Microsoft starts throttling you, it’s genuinely hard to climb back. Google Workspace will forgive you a bad week. Microsoft won’t.

If your prospect list skews Microsoft, plan for a lower ceiling and be more careful with volume, not just more patient.

New Domain vs Aged Domain vs Reactivated Account

Starting point	What the provider sees	Typical duration	The main risk
Brand new domain	No history at all	3 to 4 weeks	Reading a high day-one score as a green light
Aged domain, new mailbox	Domain trust exists, mailbox has none	3 to 4 weeks	Assuming domain trust transfers instantly
Reactivated after inactivity	A gap in the record, read like a new sender	4 weeks or more	Resuming at the old volume instead of rebuilding
Previously damaged domain	A negative history, not an empty one	4 to 6 weeks	Running a standard schedule, which makes it worse

Which Email Warmup Strategy Should You Run?

Most tools give you one ramp and that’s it. If you’re using something like TrulyInbox you get to choose. That matters more than people expect, because the right pattern depends on what stage the account is at.

AI Adaptive

The system sets daily volume itself, reading placement and engagement signals as they arrive. When placement dips it holds. When the account looks settled it climbs.

This is what I use on new accounts. It removes the daily judgement calls, and those calls are most of what people get wrong.

Progressive: The Default for New Accounts

Volume rises by a fixed increment each day, from a low floor to a set ceiling.

Predictable, boring, and right for almost every new mailbox if you’d rather drive it yourself. Start at 5 a day, add 2 or 3 a day, and cap at 50.

Randomize: Natural Variation for Warmed Accounts

Volume varies between a floor and a ceiling instead of climbing.

Nobody sends the same number of emails every day. Once an account is warm, variation looks more natural than consistency does.

Flat: Maintenance Mode for Stable Accounts

A fixed daily number, held indefinitely. This is what I switch to once outreach is running, because by then warmup’s job is maintenance rather than growth.

Picking the Right Strategy for Your Account

Account stage	Strategy	Example configuration	The “Honest” Catch
New domain or new account	AI Adaptive or Progressive	Start 5/day, increase 3/day, cap 50/day	AI Adaptive is harder to debug when something goes wrong, because the ramp isn’t yours
Completed warmup, running outreach	Flat	Fixed 30/day, replies boosted to 60%	Wrong if placement is still climbing. Stay on Progressive until it flattens
Stable, long-term production	Randomize	Min 20/day, max 40/day	Useless on anything under three months old
Reputation recovery after a drop	Progressive, from a lower floor	Start 3/day, increase 2/day, cap 40/day	Does nothing if the cause was authentication rather than volume

What Is the Best Way to Warm a New Domain for B2B Outreach?

This is how I do it, in order.

Buy your secondary domains and mailboxes at least a month in advance. Keep it to three or four mailboxes per domain. I prefer Google Workspace and Microsoft 365, but private SMTP providers work fine if you pick a reputable one.

Get the technical setup done before anything sends. SPF, DKIM and DMARC published and verified. MX records live. DNS resolving cleanly with no duplicate SPF records.

Then a custom tracking subdomain configured, and the mailbox profiles filled in with real names and signatures.

Then start warming with a reputable tool, and start slow. I run AI Adaptive because it adjusts itself, which means I’m not making a volume decision every morning.

At week four, start cold outreach while shifting warmup into maintenance.

Here’s my own configuration at that point. Switch to Flat at 30 warmup emails a day and boost the reply rate target to 60%. Then ramp cold outreach up to 30 a day.

I also set the content settings to match the kind of outreach I’m running, so the warmup mail looks like the real mail.

How to Warm Up Google Workspace, Microsoft 365 and Other Providers?

Here’s the short version: there is no separate strategy per provider. The schedule, the ratios and the gates are the same whether you’re on Google Workspace, Microsoft 365, Zoho or a private SMTP relay.

What changes is how much room for error you have, and what you do when one provider starts treating you differently from the rest.

Google Workspace

• The most forgiving of the major providers, and the most transparent.
• Connect Postmaster Tools v2 before you start. Remember that the reputation dashboards are gone — what you’re checking is compliance status and complaint rate.
• The specific Google risk is Promotions. Mail that lands there early is hard to move, so keep warmup copy plain and light on links.

Microsoft 365

• Expect 421 deferrals in week one. They’re rate limiting rather than rejection, and they resolve on their own. Don’t react to them.
• Microsoft punishes irregularity harder than it punishes volume, so hold your send window and daily count steady. It’s also the least forgiving provider once throttling starts, which is the practical reason to be conservative here rather than anywhere else.

Zoho, Amazon SES and Other Providers

• Same three-to-four-week schedule.
• Authentication alignment matters more here than anywhere. These providers give you less benefit of the doubt on a misconfigured record. More of your mail is relayed rather than sent from a mailbox.

ESP-Specific Targeting: AUTO and CUSTOM Modes

• Sometimes one provider throttles you while the others are fine. When that happens you can warm up specifically against that provider, rather than across the whole pool.
• In TrulyInbox this is the ESP prioritisation feature. AUTO matches your warmup recipient mix to the providers you actually send to.
• CUSTOM lets you set the split by hand, which is what you want when Microsoft is the one giving you trouble.

How to Split Your Warmup Volume Across Providers?

Mirror your prospect list. Pull the provider breakdown of your targets, then set the warmup split to match within about ten points. Close enough is fine here.

What Your Warmup Emails Should Actually Say

• Short, plain, and human. No links, no images, no tracking pixels in the early days. Two or three sentences is plenty.
• Write something that could plausibly be a real message between colleagues.
• Once outreach starts, match the warmup content to the kind of campaign you’re running. The two should look like they came from the same person.

How to Tell If Your Warmup Is Working

The honest answer:

Run an inbox placement test at the end of week four.

That’s the only check that tells you where your mail actually lands, rather than what a dashboard thinks of you.

Everything else is a leading indicator.

The Metrics That Matter

Metric	Target during warmup	What it means when it moves
Inbox placement rate	85%+ by week three	The only direct read on whether warmup is working
Reply rate	20%+ during warmup, 40%+ once outreach starts	Below 15% means pool quality is degrading
Spam folder rate	Under 7% week one, under 4.5% by week three	Not falling points at authentication or pool quality
Bounce rate	Under 2%	Points at list or authentication, not warmup
Trend direction	Steadily upward	One good day means nothing. The slope is the signal

Warning Signs Your Warmup Is Stalling

When any of these show up, hold volume steady and investigate. Pushing through compounds it.

• Inbox placement flat below target for five or more consecutive days
• Rising 421 deferrals from Microsoft
• A sudden spam-rate spike after a clean run
• Reply rate falling as volume rises

How to Measure Inbox Placement?

Inbox placement rate is inbox divided by total emails sent. That’s it.

• A seed-list test is the reliable version. Send to a known set of mailboxes across the providers you care about, then count where each message landed.
• Run it at week four, and again a fortnight after outreach starts.
• Dashboard scores are useful for spotting a trend, but they’re an estimate, and the test is the measurement.

Does Email Warmup Actually Work?

Yes, and we can show you where it stops working too.

Why Your Cold Emails Still Go To Spam?

Warmup fixes one variable, and cold email deliverability has several. These are the ones we see most.

• The list is scraped, so bounces and complaints arrive regardless of sender reputation
• Volume jumped the moment warmup ended, breaking the pattern providers had learned
• Warmup stopped when outreach started, removing every positive signal at once
• Authentication is incomplete, which as our test showed only surfaces at higher volume
• A shared tracking domain carries someone else’s reputation into your mail
• The domain has prior damage, so providers are reading a negative history rather than an empty one

The second and third are the common reasons for emails landing in spam, and they usually happen together.

What Warmup Tools Actually Do for You?

• They produce consistent positive engagement at a volume and regularity no human sustains by hand.
• That’s the entire value, and it’s enough. Consistency is what moves reputation. Consistency is exactly what people fail at.
• We looked at this with our partners at Saleshandy across accounts running live outreach. 

When Warmup Will Not Help You?

• When the problem sits outside warmup: a purchased list, broken authentication, spam-triggering copy, or a domain with real history against it.
• A previously damaged domain is the hardest case. Recovery runs four to six weeks where it works at all.
• A standard schedule on a badly burned domain can make things worse, so price a fresh domain against the expected recovery time before committing.

What Happens After Warmup? The Transition and Recovery

Technically, there is no “after warmup“.

Warmup runs before outreach, during outreach and after outreach. It isn’t a phase you complete and switch off.

It’s a signal you keep generating, and its job changes at each stage.

Stage	What warmup is doing	Volume	Ratio to outreach
Before outreach	Building reputation from nothing	5/day climbing to 50/day over 4 weeks	No outreach yet
During outreach	Maintaining reputation against cold-mail drag	50 to 60/day	At least 2:1 warmup to outreach
After a campaign	Rebuilding what outreach cost you	Hold at 50 to 60/day	Raise the ratio until placement recovers

Why the Transition Is More Dangerous Than Warmup

• Most deliverability failures we see arrive in the days after outreach starts, not during warmup.
• You spend four weeks teaching providers that you send 50 careful, well-received messages a day.
• Then you switch on a campaign, send 200 cold ones, and turn warmup off because it looks finished. Every positive signal disappears on the same morning a pile of unanswered mail appears.

The Transition Schedule

Change the composition of your sending, not the volume.

Phase	Warmup volume	Cold outreach	Ratio	Duration
End of week 4	50/day	0	—	Until the placement test passes
Outreach week 1	50 to 60/day	10 to 15/day	Roughly 4:1	5 to 7 days
Outreach week 2	50 to 60/day	25 to 30/day	Roughly 2:1	5 to 7 days
Steady state	50 to 60/day	30/day	2:1	Ongoing

Notice that warmup volume never comes down. That’s the point.

Our own experiment and the Saleshandy study agree: the 2:1 ratio is what holds placement together once cold mail enters the picture.

How to Know When You Are Ready for Outreach?

• An inbox placement test at week four that comes back at 85% or better. Zero bounces across the previous week. Placement trending up rather than flat.
• Miss any one of those and hold another week. The week costs less than the recovery does, every time.

Maintenance Warmup and When to Re-Warm an Account

• Keep warmup running permanently, because reputation decays without positive signal. The account that’s been warming for months is the one that survives a bad campaign.
• Rebuild from a lower volume after any gap of a month or more. Same after any placement drop you had to fix.

What to Do When Deliverability Drops After Warmup?

• Don’t restart from zero. That’s the instinct, and it’s wrong.
• Cut cold volume by half, hold warmup where it is, and let the ratio move in warmup’s favour.

Keep everything else still: same times, same copy, same list quality. Then give it a week. If the cause was behavioural, recovery usually shows within days.

Warming Up Multiple Email Accounts at Scale

Rules for Warming Up Multiple Accounts

You don’t need to stagger start dates. Starting a batch of mailboxes on the same day is fine.

The tidiness of one start date is worth more than any theoretical benefit from spreading them out.

The real problems at scale are different:

• Monitoring: A fleet average hides the one account that’s failing, and that’s the account that will damage the domain
• Cost: Most warmup tools charge per inbox, so the bill scales with mailboxes rather than with usage
• Connection effort: Adding thirty mailboxes by hand, one OAuth consent at a time, is its own tax

Keep three or four mailboxes per domain and spread across several domains, because providers correlate behaviour across mailboxes that share one.

What Warmup Costs Across a Fleet of Mailboxes?

• Per-inbox pricing is fine at three mailboxes and painful at thirty.
• Worse, it charges you more for doing the right thing: spreading sending across more mailboxes at lower volume each.
• TrulyInbox charges on warmup email volume rather than per mailbox, so adding mailboxes to spread your sending doesn’t multiply the bill.

Manual vs Automated Warmup

Manual warmup works for one or two mailboxes, if you can genuinely reply daily for three weeks. Most people can’t. A missed week costs more than the fortnight before it earned.

Past a handful of accounts, the constraint stops being discipline and becomes arithmetic. Generating enough real replies by hand across a dozen mailboxes isn’t something anyone does alongside a job.

At that point what matters is what your tool can automate. TrulyInbox has a fairly extensive API, and these are the parts worth knowing about:

• Workspace bulk connect — register a Google Workspace or Microsoft tenant, preview its mailboxes, and sync them in, rather than connecting one at a time
• Email account management — connect, disconnect and list mailboxes, including an OAuth consent link for a single Microsoft mailbox, plus bulk delete and status checks
• Warmup control — start and stop warmup, change settings, run bulk actions, and pull activity history
• Deliverability checks — setup scores, refreshes and DNS validation
• Reporting — single-account and bulk reports, exports, and an account-wide dashboard

It’s also one of the few platforms offering domain-wide delegation through the API. You connect a whole domain and every mailbox under it in one move, rather than mailbox by mailbox.

The Email Warmup Mistakes That Cost the Most

Ranked by how expensive they are to undo:

1. Sending bulk outreach from your primary domain
2. Hitting spam traps from a scraped list
3. Starting outreach after one week because the dashboard score looked good
4. Turning warmup off the day campaigns go live
5. Ignoring bounces while volume climbs

The first two burn a domain. The middle one is the most common by a distance, and the last two cost you weeks.

We cover each of them, and how to recover, in common email warmup mistakes to avoid.

Choosing an Email Warmup Tool

Judge a warmup tool on five things, in this order.

• Pool quality — who are you exchanging mail with, and are they real active mailboxes? This is the one nobody advertises and the one that decides everything
• Pricing model — per inbox or per volume. At any scale beyond a few mailboxes this is the difference between affordable and not
• Strategy control — can you pick how the ramp behaves, and change it when the account stage changes?
• Provider targeting — can you warm against a specific provider when one starts throttling you?
• API and bulk connection — can you connect a whole domain, and pull reports for every mailbox, without clicking through thirty consent screens?

Feature lists look similar across every vendor. The five above are where they actually differ, and where the money goes.

Choosing an Email Warmup Tool? 

Read this – Email Warmup Services Comparison

Frequently Asked Questions About Email Warmup

1. What is email warmup?

Email warmup gradually sends and receives mail from a new or inactive account, building sender reputation before real outreach starts. Providers let your early mail through so they can evaluate you, and warmup makes sure what they see is positive.

2. How long does email warmup take?

Three to four weeks for a new account on a new domain, and four to six if the domain has damaged reputation. Our data shows placement climbing to 86.3% by week three.

3. Does email warmup actually work?

Yes, within limits. It reliably improves where your mail lands when an account starts or restarts sending. It can’t override broken authentication, a blacklisted domain, a scraped list or spammy copy.

4. How many warmup emails should I send per day?

Start at 5 a day and increase by two or three daily, reaching 50 by the end of week four. Cap at 50 to 60 a day. There’s no benefit to going higher.

5. My deliverability score says 90% after one week. Can I start outreach?

No, and this is the most expensive mistake we see. New accounts often start high because providers are still evaluating you. Let the full three to four weeks run, then confirm with an inbox placement test.

6. Should I keep warmup running after I start cold outreach?

Yes, at a ratio of at least two warmup emails for every cold one. Our joint study with Saleshandy found accounts that stopped warmup lost placement significantly faster than those that kept it running.

7. What is the difference between email warmup, domain warmup, SMTP warmup and IP warmup?

They’re four names for the same activity. Warming your mailboxes builds mailbox reputation, and doing it across a domain builds the domain’s reputation too. SMTP warmup just means warming mailboxes that send over a relay.

8. Do I really need SPF, DKIM and DMARC?

Yes. In our own test, accounts with incomplete records looked fine for ten days. They then dropped to the 70 to 80% placement range at week two and stayed there. Microsoft is the strictest about it. Here is how to set up all three.

9. Which provider is hardest to warm up on?

Microsoft 365. Across our paid accounts it places 79.0% against Google Workspace’s 91.5%, with double the spam rate. It’s also the hardest to recover with once throttling starts.

10. How do I know if my warmup is working?

Run an inbox placement test at the end of week four. Dashboard scores are a useful trend indicator, but a seed-list test is the actual measurement.

11. What reply rate should my warmup have?

Above 20% during warmup, and above 40% once cold outreach starts. The higher figure offsets the silence from cold mail, which otherwise drags the account’s overall engagement down.

12. Can I warm up a Google Workspace or Microsoft 365 account?

Both need it and both respond. The schedule is identical. Google is more forgiving of a bad week, and Google Postmaster Tools v2 gives you compliance visibility that Microsoft doesn’t match.

13. Do I need to stagger warmup start dates across mailboxes?

No. Starting a batch together is fine. What matters more is keeping three or four mailboxes per domain, spreading across domains, and monitoring each account rather than the fleet average.

14. What should I do if deliverability drops after warmup?

Halve your cold volume, hold warmup where it is, and change nothing else. Most post-warmup drops are a volume or timing discontinuity rather than a reputation verdict, and recovery usually shows within days.