So you’ve spent a lot of time writing the perfect welcome email, or perhaps you’re just trying to send a quick inquiry. You’re ready to move on to the next thing on your list—but wait—your email has come back with a “Message not delivered” warning. Uh-oh.

As annoying as it is, there is generally a quick fix. We’ve provided a checklist, starting with the easiest fixes and moving on to the more complicated ones, to help you get that mail out of your hair and into the recipient’s inbox where it belongs.

Why Are My Emails Not Being Received?

  1Invalid email addressConfirm address with the recipient; check for typos
  2The recipients’ mailbox Is fullContact them to let them know. If urgent, use another form of communication.
  3Server Issues – Network disruptions, maintenance or internet downBe patient! And try again later.
  4Email attachments too large/flaggedReduce size; use a cloud service like Dropbox.
  5Overly strict email rules & filtersApply email best practices so your email isn’t rejected.
  6Email is in the Spam FolderApply email best practices so your email isn’t rejected; Use an email deliverability tool.
  7Malware AttackRun antivirus software & immediately change email passwords.
  8IP has been blacklistedDetermine the reason for your IP being blacklisted, make necessary changes & then contact the blacklist provider to request removal.
  9Failure to Comply With PoliciesCheck all DMARC, SPF & DKIM polices.


Please read on for more information on causes and how to fix them.

1. Invalid E-mail Address

While we’re all used to Google auto-correcting our typos, if you make a mistake with the recipient’s email address, there is no auto-correct to save you. You won’t believe how often these little typos creep in, and when they do, you’ll receive an error message.

As you’ve probably noticed, the warning message is not always very specific (which is why you’re here). Make sure you’ve entered the correct email address—this is the easiest place to start.

By the way, have you checked to see if your email was actually sent? Maybe in your rush, you didn’t click the send button. Check for the email in your sent mail folder to be sure.

2. Recipients’ Mailbox Is Full

Another easy fix. However, most email providers now give their users enough storage, so this issue is less frequent than it used to be. Even a free Gmail account comes with 15GB of storage.

But if you do encounter this issue, you can call the person or contact them at an alternative email address to advise them. (Plus, this makes you seem really helpful; well done you!).

The recipient will need to delete messages from the mailbox to free up space in their email account.

A recipient deleting messages from mailbox to free up space in their email account.Courtesy of Canva/Wichayada

3. Server Issues

This issue can occur due to server maintenance, unexpected downtime, or network disruptions. It’s advisable to wait and retry sending the email after some time.

Meanwhile, alternative communication methods such as phone calls or social media can be used to ensure timely communication. If the problem persists, it may be beneficial to contact the recipient through other means to confirm the best way to resend the information.

4. A problematic email attachment

Even though common file types like Word documents, PDFs, and Excel spreadsheets typically pass through, they can encounter issues. Especially when an attachment contains macros.

Emails that include .docm (macro-enabled Word files) or .xlsm (macro-enabled Excel files) could be blocked. Similarly, compressed (zipped) files may also encounter restrictions.

First things first, check the limit and size of the attachment. If that’s okay, scan the attachment for malware. Then try to save the attachment using a different file type. For example, convert an Excel file to a PDF document, and lastly, if all else fails, rather share the attachment using a cloud storage link.

Okay, so there are your easy fixes. Let’s continue with solutions that will require a bit more work from your side.

5. Email Rules and Filters 

Users can set specific rules for incoming and outgoing messages –  that automatically redirect, delete or block certain emails. If a recipient has stringent rules set up, these can inadvertently prevent your emails from being delivered.

For example, emails that come across as too promotional or pushy (this can even include too many exclamation marks!!! Or capital letters) can be set to go straight to spam.

The best way around this is to write good copy that’s engaging but not too salesy, compelling but not pushy. And definitely leave exclamation marks and CAPS out of your email campaign.

Young man engage in email campaign with compelling text "Email Sent But Not Received By Recipient"

Okay, so there are your easy fixes. Let’s continue with solutions that will require a bit more work from your side.

6. Your Email is in the Spam Folder

In 2023, spam made up a whopping 45.6% of all email sent worldwide. [1]

So email service providers have advanced SPAM filters that distinguish between legal and fraudulent emails. However, they don’t always get it right. Occasionally, email providers intercept genuine emails.

So, ask your recipient to check their junk folder and mark it as safe to prevent this from happening again.

You should also try a  few of these easy fixes – we call them email best practices. These include:

  • Avoid using certain words or phrases that trigger spam filters
  • Avoid using an excessive amount of links
  • Avoid spammy subject lines. Ditch lines like “!!!ACT NOW!!! Claim Your FREE Gift Card Worth $500 – Limited Time Offer!!!” and try these ideas instead.
  • Always include an unsubscribe option.

Ensure your emails always hit the inbox, not the spam folder! Try InboxAlly’s Deliverability Tool today to boost your email deliverability rates. InboxAlly optimizes your email settings and practices to enhance your sender reputation, helping you avoid the SPAM folder.

Related: Free email spam checker

7. Malware Attack

What happens if you get a “Mail Delivery Failure” alert for interactions you never sent?

It’s possible you were the victim of a malware attack. More specifically, a virus is using your account to send spam emails. Not good.

The presence of malware not only disrupts your regular email communication by flooding your inbox with bounce-back messages, but it also poses serious security risks. Your email account being used in this way can lead to blacklisting by email servers, which further affects your ability to send legitimate emails.

Our advice? Immediately scan your computer using anti-virus software, remove any detected threats and change your email account password ASAP.

Man touching a digital screen displaying an email icon with a checkmark, on a laptop at a desk, with glasses and a coffee cup nearby.Courtesy of Canva/Svetazi

8. Your IP Has Been Blacklisted

This is probably the most frustrating problem on the list, but not impossible to fix. First things first, you want to check if you have indeed been blacklisted. This can be done using a free tool like MX Toolbox.

If your IP address is blacklisted by the recipient’s mail server, you’ll need to figure out why. Once the problem is fixed, you can then contact the blacklist provider to request removal. This process can take anywhere from a few hours to several days.

Related: What is IP blacklisting?

9. Failure to Comply With Policies

Mail providers use policies like SPF, DKIM, and DMARC to verify the authenticity of the sending server.

What’s the big deal with all these policies? Proper configuration of SPF, DKIM, and DMARC not only builds trust with email servers, reducing the likelihood of emails being marked as spam but also improves your reputation among email service providers.

As a result, your emails are more likely to arrive in the intended inboxes rather than being redirected to spam folders or rejected altogether. Here’s a quick breakdown of each policy:

  • SPF (Sender Policy Framework): This DNS record tells which servers can send email on your domain’s behalf.

If you already have an SPF record, use MX Toolbox to check that it is valid and doesn’t exceed the DNS lookup limits. If you still need to set one up, ensure it correctly lists all your mail servers.

  • DMARC (Domain-based Message Authentication, Reporting & Conformance): Specifies how your email is verified and what should happen if it doesn’t pass the checks.

You can easily create a record using a DMARC record tool.

  • DKIM (DomainKeys Identified Mail): Uses a digital signature to let the receiver of an email know that the message was sent and authorized by the owner of a domain.

Related: SPF, DKIM, DMARC explained.


A joyful woman at a desk with her laptop, raising her fists in victory after identify reasons why her email is sent but not received by the recipient.

Okay, so hopefully, you’ve been able to identify the cause of your email not being received. It could have been an easy fix like checking their email address (in which case you’re probably not still reading this) or something more complicated like your emails going to spam.

If this is something that happens regularly, our email deliverability tool is designed to fix this. InboxAlly teaches email providers to put your messages in the Inbox – From the start.

We work to improve your reputation by engaging with your email content when it’s sent to our “seed emails.” These seed emails help train mail providers to see your content as valuable and to prioritize delivery to the inbox.

Say goodbye to email deliverability issues for good! If this sounds like what you need, reach out and contact us or read further about how InboxAlly works.