Email Delivery Failed: 4 Tips to Fix Problems

Email delivery failed messages can be frustrating. Not only do they indicate that there is a problem with your email marketing campaign, but they can also hurt your sender reputation and make it difficult for your recipients to receive your messages in the future. In this blog post, I will discuss why email delivery failed messages occur, and how you can fix them. I’ll also provide tips on how to reduce email complaints, bounces, and improve email message quality. Learn how to get your message in front of more eyes!

Did you know that in 2022 there were about 333.2 billion email messages sent per day, and that in 2025 that number is projected to increase to 376.4 billion messages? Given the population of all humans on the planet for 2022 was 7.9 billion people, that would equate to about 42 billion email messages per person, per day.

While many (including myself) might wonder where those extra email messages are going (after all, I don’t think any of us receive 42 billion email messages per day), the real focus for us should be consider the shear volume of email traffic, and how we can ensure our email get’s through, without the dreaded “email delivery failed” scenario.

Before we move forward, if you’re anything like me, you’ll still wonder where all that “extra” email is going to? I had to dig a little deeper. It turns out, according to Statistica, in 2021 spam accounted for about 283 billion. Don’t forget, a significant number of additional email sent will result in other failures.

How do we ensure our email campaigns can neatly avoid email delivery failed issues?

Reduce Your Email Complaint and Bounce Rate

When your email campaign messages get sent to the wrong people or are caught in spam filters, this can result in increased spam complaints. This can happen in two ways:

  1. Automated (email application or server based) systems that flag the message and in some cases automatically take reporting action.
  2. Manual actions of the recipient, where they can click or tap a button to report spam complaints. In some cases (although I don’t see this as much), people can contact their ISP or ESP (email service provider).

It’s also important to note, email that is bounced for spam will be recorded as such, and this will negatively impact your reputation.

Increased complaint rates is one of the highest reasons that contribute to your failed email delivery rate – The more complaints, the worse the reputation, the less recipient networks will accept your email.

This begs the question… How can we enhance the integrity of our mailing list addresses (to help reduce spam complaints)?

Leverage Feedback Loops

A feedback loop is an automated tool that provides you with the email addresses that reported a complaint. It’s useful because this allows you to prune those email addresses out of your email list (which avoids further complaints).

For example Amazon SES has a system where bounced email, and spam (reported) email is immediately added to a suppression list (so further sending to that email address won’t occur). This provides you the time to later remove the email address at your convenience. You can also manually add (or remove) addresses from this list.

Email Delivery Failed Metrics.

Below is an example of some snippets (redacted for privacy) of a bounce message feedback they would send you:

notificationType”:”Bounce”,”bounce”:{“feedbackId”:”0000000000000000-00000000-1cde-4ca8-bd5d-57d68310f367-000000″,”bounceType“:”Permanent“,”bounceSubType”:”General”,”bouncedRecipients”:[{“emailAddress“:”“,”action”:”failed“,”status“:”5.1.1“,”diagnosticCode”:”smtp; 550-5.1.1 The email account that you tried to reach does not exist. Please try\n550-5.1.1 double-checking the recipient’s email address for typos or\n550-5.1.1 unnecessary spaces. Learn more at\n550 5.1.1

This immediately adds the message to the suppression list (so your email reputation does not decline further).

Then, the next time your email campaign tries to send an email to that same email address, the returned message will advise that the email account (you tried to send to again), did not get sent:

notificationType”:”Bounce”,”bounce”:{“feedbackId”:”0000000000000000-00000000-2877-49f0-9046-f2b7329cbb55-000000″,”bounceType”:”Permanent”,”bounceSubType”:”OnAccountSuppressionList”,”bouncedRecipients”:[{“emailAddress”:”“,”action”:”failed”,”status”:”5.1.1″,”diagnosticCode”:”Amazon SES did not send the message to this address because it is on the suppression list for your account. For more information about removing addresses from the suppression list, see the Amazon SES Developer Guide at

In my opinion, this is a nice way of automating a feedback loop, as it helps to keep the existing delivery attempts accurate (clean), whilst letting me remove (bad) email addresses from the list later.

Strengthen Your Email Services

In my experience, there tends to be three generalized types of email marketing:

1) Using an existing ESP service.

In my opinion reaching out to, and using a dedicated ESP is the way to go. In the long run you’ll get let email delivery failed messages, and the overall costs will be cheaper.

Also your ESP will better provide the tools to handle permissions, CAN-SPAM, CASL, GDPR, etc.

If there is a disaster, the ESP will be able to restore faster.

Further, if there is a complaint, the communication process (to resolution) is often faster as it may be possible of the ESP to remediate at their end.

2) Building out a “private” email system.

Building out a private emailing system is expensive, and over time the maintenance / upkeep costs can become especially high, particularly when working to recover from an RBL (real time blocklist) listing.

3) Using a “semi-private” plugin (as in WordPress, connecting to an ESP).

Using plugins to maintain your own email list (such as those WordPress users can install), and relaying email over a bonafide ESP, is not something I’d recommend, as it can come with some significant drawbacks:

  • If your database goes down, it takes your valuable email list with it.
  • If you’re challenged, you may have difficulty providing evidence of permissions (to send email to specific users).
  • It can add excessive load to your website (causing it to operate slower). This contributes to a poorer user experience.
  • If there’s an issue, mail relaying can be suspended, and you’ll be the one who needs to show-cause why services should be restored.
  • In practise, emailing services and website hosting services should be kept separated. This way, an issue with one, does not effect the other.
  • Statistics for these types of plugins are kept in the same database as your website – Causing needless bloat (and the potential for issues as your email list grows increasingly larger).

Here’s why (ultimately) I’d advise using an ESP service

Whether you’re using Mailchimp, MooSend, Drip, or any number of a large list of ESPs, they’ll generally help you with the following:

  • Email servers are properly configured, and managed. If there is an issue, they can simply switch which servers email is routed though (so your email campaign continues to send email).
  • They have ant-spam measures in place, so you’ll see less email delivery failed type messages, and more successful deliveries, because they will already have servers with a good sending reputation, in use.
  • Your emailing functions (and mailing list management) are offloaded, so you’ll see less negative impact to your existing website and related marketing efforts.
  • They will have feedback loop tools in place, to further mitigate bounce and spam complaint challenges.
  • They’ll better help you ensure compliance with email and privacy related legislation.
  • Better tracking and reporting tools are available, that you can use to improve your content, better segment your list, prune your email list, and so on.

Build Permission Based Email Lists

A powerful (and useful) email list should always ask subscribers for permission – Period! People who subscribe, with permission, want your email.

I think it’s become obvious why simply blasting email to every email address you can find is a direct route into people’s spam boxes, and an increase in email delivery failed messages.

To that end, maintaining an effective and strong opt-in solution, helps build a better long term, engage email audience.

Once a subscriber opts-in, it’s important to keep abreast of updates – People change over time, and your email list needs to change as well. Stale email addresses (where there are no opens, clicks, etc.) should be pruned out. Sometimes people update to a new email address, again, you’ll see an increase in bounces to old email addresses (and you should update right away).

And here’s a real kicker…

When you get to the inbox of your subscribers, their ISP’s pay attention to the engagement rate of your email!

This is a clear signal that to help reduce email delivery failed type messages (spam related or otherwise), your email list must position itself for engagement!

Subscribers that aren’t opening your emails indicate to the ISPs that they don’t want them, and you start to resemble spam – And eventually have trouble reaching new or existing subscribers on the same network (examples: <someone>, and so on).

Better segment your lists, test and optimize your subject lines, then send tailored, relevant, timely content to your subscribers so that you can better interact with them to reduce email delivery failed messages. Stands to reason… Your email must provide value!

Fixing Error Messages

It’s important to pay attention to email delivery error messages because they indicate a problem with either the email address, the email server, or the email content. You should fix them quickly to reduce the number of email delivery failed messages that you send.

Email Complaints

An email complaint is a message that is sent to the email server or email client, usually by the recipient, about a particular email. The email client then records the complaint and takes appropriate action, such as returning the email to the sender, deleting it, or flagging it as spam.

Ideally, you want to keep email complaints below 0.1% – Anything above that can indicate a problem. And in many cases can result in no email being relayed to your list subscribers.

When a complaint is returned, immediately remove that subscriber from the list, then troubleshoot the issue )in case it’s something that may cascade to other subscribers).

It helps to include a note as to why subscribers are receiving your email – This especially useful (as a reminder) for lists that don’t send very often.

Email Bounces

An email bounce is a notification that an email sent to a recipient was not delivered. The email may have been rejected by the recipient’s email server, or it may have never reached the recipient’s email server.

There are two types of email bounces: soft bounces and hard bounces.

A soft bounce is a notification that an email was not delivered because the recipient’s email server was temporarily unavailable.

A hard bounce is a notification that an email was permanently rejected by the recipient’s email server because the email address is invalid.

Ideally, you want to keep your bounce rate well below 10% (which is a higher rate, try shooting of 1% or less) – Anything above that can indicate a problem with your list (or email content).

When a bounce is returned, immediately remove that subscriber from the list.

It’s important to pay attention to bounce email delivery failed error messages because they indicate a problem with the address, server used, or the email content itself. You should fix them quickly to reduce the number of email delivery failed messages received.

Email Message Quality

Poor quality email content can lead to email delivery failed messages. This is because the email content may not be relevant to the recipients, or it may be considered as spammy.

You can improve email content quality by:

  • Writing clear, concise subject lines
  • Using relevant, timely, and tailored content
  • Testing and optimizing your email content
  • Using images, videos, and other multimedia content sparingly

This helps avoid spam filters. It also is a better approach to ISP engagement monitoring. Generally, the more engaging your email is, the less email delivery failed messages you receive.


How do I fix mail delivery failure?

A very generalized answer: First, you should check the email address to make sure that it’s correct. Next, you should check the email server to make sure that it’s available. Lastly, you should check the email content to make sure that it’s correct. If you’re still having trouble, you can try contacting the email server administrator or the email client administrator.

Why do I get mail delivery failure messages?

There are a number of reasons why you might be receiving email delivery failed messages, but some of the most common causes are:

– Invalid email address.
– Email server is unavailable.
– Email content is seen as spam or not relevant recipients.
– Email content is not well-written or clear.
– Email subject line is not relevant or interesting with.

You can improve your email deliverability by paying attention to these factors and making sure that your email content is high quality and relevant to your recipients. You can also try contacting the email server administrator or the email client administrator if you’re still having trouble.


Email delivery failed messages can be caused by a number of factors, including invalid email addresses, email server unavailability, spammy or irrelevant email content, and poor email writing quality. However, you can take steps to improve your email deliverability rates by paying attention to these factors and ensuring that your email content is high quality and relevant to your recipients. Doing so helps reduce email delivery failed messages to a minimum.

You can learn much more about email delivery optimization by visiting our Small Business Email Marketing posts. As well as find out more about Email Delivery.


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