Vatsal Shah The first goal of sending an email is simple — get your emails in the inboxes of your recipients.
But what if your emails don’t even make it into your recipients MAILBOX – not the spam folder, not the promotions tab, nowhere at all?
Maybe instead of a reply, you got an email from the infamous “Mail Delivery Subsystem” or “MicrosoftExchange”, saying your message couldn’t be delivered.
Sounds familiar?
Then you have just faced an email delivery issue, and your email failed to get delivered to your recipients.
So, why does this happen and how can you fix this?
That’s what I am going to answer in this blog!!
I’ve put together a list of the 10 most common email delivery issues — and how you can solve each one of them.
So, keep reading!
Top Email Delivery Issues – TOC
What is Email Delivery Failure?
When you send an email, and it does not reach its destination – your recipient’s mailbox, then you just had an email delivery issue or email delivery failure.
By mailbox, I mean any of the tabs or folders in their email account — Primary Inbox, Spam, Promotions, Social, Updates, or anything else.
(RIP Email 🪦)
FYI:
Email delivery and email deliverability are two different things:
- Email delivery is about whether your email reached the recipient’s mailbox at all.
- Email deliverability is about where it landed once it got there — inbox, spam, or elsewhere
So, how would you know if you have email delivery issues?
Well, you’d get an email saying your message couldn’t be delivered. Simple!
10 Reasons Why Your Emails Are Not Delivered
There are quite a few reasons why you may be facing email delivery issues.
After a lot of research, I found the 10 most common reasons why you might be experiencing email delivery failure:
- You Sent an Email to an Invalid Email Address
- Your Authentication Records May Not Be Set Up Properly
- Your Recipient’s Mailbox May Be Full
- You May Have Hit Your Daily Sending Limit
- You Are Not Complying With ESP Regulations
- You Are Being Blocked by Spam Filters
- You May Have Been Blacklisted
- Problems With Your Email Infrastructure
- Server Configuration of Your Recipients
- Temporary Server Issues
I’ve also included quick fixes for each of these issues.
Check them out one by one and fix your email delivery issues.
1. You Sent an Email to an Invalid Email Address
Let’s start with the most common cause of email delivery failure: Sending email to an invalid/incorrect email address
“If an email address doesn’t exist… then where is the email supposed to go? 🫠”
In such a situation, your email bounces back, and you get an email from the Mail Delivery Subsystem saying the address was not found.
This can happen because of 2 reasons:
- You may have made a typo – maybe you missed a letter, added an extra dot, or just messed up the domain name.
(I’m guilty of typing gmial.com instead of gmail.com 🙈) - You sourced your email list from somewhere unreliable — and it includes fake, inactive, or outdated email addresses.
What Should You Do to Fix This?
The fix is simple:
- Re-check your recipients’ email addresses before hitting the send button.
- Source your email list from a reputable B2B Business Databases.
Pro Tip:
I always recommend cleaning your email list using email verification tools like ZeroBounce or MillionVerifier, even if you build your email list from a trusted data platform.
2. Your Authentication Records May Not Be Set Up Properly
Having your email authentication records is a must, especially for B2B email communication, marketing or sales outreach, etc.
These records – SPF, DKIM, and DMARC, actually protect you and your recipients from spammers, spoofers, and phishing attacks.
Setting them up is quite easy, but one small mistake – a missed semicolon or a misconfigured entry can cause delivery problems.
What Should You Do to Fix This?
Check if you have set up your SPF, DKIM, and DMARC records properly.
You can use these free tools to check and verify if your records are set up correctly:
Pro Tip:
If you are just starting out, I recommend you set your authentication policies to a relaxed or monitoring mode (like p=none for DMARC).
3. Your Recipient’s Mailbox May Be Full
Sometimes it’s not you, but your recipient!
Although rare, I’ve actually faced this a couple of times — my recipients had simply run out of space to store emails!
When their mailbox is full, their server can’t accept any new messages, so your email bounces back with errors like:
- Mailbox full
- User is over quota
- 552 storage allocation exceeded
What Should You Do to Fix This?
Unfortunately, there’s no workaround to this problem.
I mean, you can’t call them and be like, “Hey, I want to send you an email — can you please delete a few old ones?” 😅
If you must reach out to such prospects, I’d suggest you try other channels like LinkedIn, or a phone call if you have their number.
4. You May Have Hit Your Daily Sending Limit
Every ESP imposes limits on the number of emails you can send in a 24-hour period.
For example:
- Gmail allows 500 emails/day for standard accounts
- Gmail Workspace allows up to 2,000 emails/day
- Other ESPs (like Outlook, Zoho, Yahoo, etc.) have their own limits too
So, the moment you exceed the limit, your emails will either fail to send or they’ll get queued to be delivered after the 24-hour window.
What Should You Do to Fix This?
If you want to send more emails – buy more email accounts!
That’s what I did during my cold outreach days.
More Accounts = More Sending Capacity = Fewer Delivery and Deliverability Issues.
5. You Are Not Complying With ESP Regulations
Compliance is non-negotiable!
If you’re not playing by the rules set by your ESP (Email Service Provider – Google, Microsoft, Zoho, etc.), you’ll definitely get blocked by them.
For instance, Google and Yahoo guidelines specify that all bulk email senders need to have their SPF and DKIM records set up and aligned with a DMARC record.
You’ll also have to:
- Include a visible unsubscribe link if you’re sending sales or marketing emails.
- Keep your spam complaint rate below 0.3%
- Make sure you don’t send mass, spammy emails,
- Plus, more.
What Should You Do to Fix This?
Comply with your ESP guidelines and follow best practices, and you’ll be good to go.
6. You Are Being Blocked by Spam Filters
Spam filters can do much more than just direct your email to the spam folder.
In fact, they can even block your email from being delivered at all!
As malicious users have discovered more ways to bypass spam filters, the filters themselves have improved in scope and ability.
In short, spam filters are on the lookout for anything that resembles suspicious email-sending behavior.
So, if you’re sending emails with spammy words, links, or attachments, there’s a high chance that your email will be flagged by the spam filters.
What Should You Do to Fix This?
I’ve had a lot of success with bypassing spam filters by following a set of best practices for bulk emailing:
- Use simple text instead of HTML scripts in your emails
- Don’t include links in your emails
- Don’t send emails with attachments
- Personalize your emails so that the ESP doesn’t detect a generic email pattern
7. You May Have Been Blacklisted
If you’ve tried and tested all the fixes we’ve listed above, but your email delivery has still not improved, there’s a chance that you may have been blacklisted (or blocklisted) by your ESP.
Spam blacklists are created and curated by ESPs and cybersecurity enterprises.
They contain a list of email accounts or domains that the ESP or other institutions don’t trust to deliver engaging and meaningful content.
So, if you’ve fixed every other problem but aren’t able to stop poor email delivery, you can try to explore the Blacklists of the leading ESPs and cybersecurity firms.
What Should You Do to Fix This?
Truth be told, it’s really difficult to get an email account off a spam blacklist.
(Impossible actually 😣)
All you can do is get new domains and email accounts.
If you don’t want this to happen, I recommend you regularly track key email deliverability metrics and take proactive action when things look like they are going south.
8. Problems With Your Email Infrastructure
Sometimes the issue lies deeper than you think…
At times, the infrastructure setup on your end — the part that actually sends the emails — might be the real problem.
If your email is going out through a misconfigured SMTP server, an IP with a poor reputation, or an outdated setup, etc., your email may never make it to the recipient’s mailbox.
This usually happens when:
- You’re using a self-hosted email server without proper authentication
- Your DNS records aren’t correctly configured
- Your IP address has been shared or blacklisted
- You don’t have proper security protocols like SSL or TLS in place
What Should You Do to Fix This?
The easiest way to fix the problems with your email infrastructure is to conduct an audit of the existing ecosystem and troubleshoot any problems that might arise.
It involves collecting deliverability data (such as spam rates and bounce rates) and then fixing individual problems like email authentication, spam usage, and ESP sending requirements.
9. Server Configuration of Your Recipients
Just as your email ecosystem might have some issues leading to poor delivery, the same can happen on your recipient’s side too.
Sometimes, your email is totally fine — it’s written well, authenticated properly, and sent from a clean IP — but the recipient’s mail server is misconfigured or set up too aggressively.
What Should You Do to Fix This?
Well, here, you can’t do much, as their email setup is out of your control!
My Suggestion:
Approach them through a different channel, share your experience, and wait for a response.
10. Temporary Server Issues
The last issue on my list is Temporary Server Outage.
This is a very, very, extremely rare scenario — especially if you’re using a well-known, reputed ESP like Google, Microsoft, Zoho, or any established email provider.
But hey, tech can act up sometimes.
Even the best servers need maintenance or might face temporary downtimes due to high traffic, internal errors, or network issues.
What Should You Do to Fix This?
Unless you can fly in and sort the servers yourself (which would be impressive 😅),
there’s honestly not much you can do.
Just wait it out — most issues like this resolve on their own. You can try resending your emails after a few hours
Don’t Face Email Delivery Failure Anymore!
There you go! I’ve covered the 10 most common reasons for email delivery issues — along with practical fixes for each one.
I hope you’re able to spot and fix what’s blocking your emails, and finally get them where they’re supposed to go — your recipient’s inbox.
Happy getting your emails delivered to inboxes!
Email Delivery Issues: FAQs
1. What is the difference between email delivery and email deliverability?
Email delivery is about whether your email reaches the recipient’s mailbox at all.
If it bounces back or gets blocked — that’s a delivery failure.
Email deliverability, on the other hand, is about where the email lands after it’s delivered — inbox, spam, promotions, or somewhere else.
2. Can I improve my email delivery and deliverability at the same time?
Yes, 100%! In fact, most best practices help with both:
- Set up SPF, DKIM, and DMARC
- Send emails from a reputable domain and IP
- Avoid spammy content
- Keep your list clean and up-to-date
- Comply with ESP regulations
- Send to people who actually want your emails
By following these, you can make sure your emails are delivered in your recipient’s inboxes.
