• Best Practices

Email Bounces: What To Do About Them

Mailgun Team
5 min read

What Are Email Bounces?

Email bounces — When email messages cannot be delivered to an email address. There are many different possibilities for an email bouncing, so as a result a "return to sender" message is applied, also called a "SMTP Reply" is sent from the recipient's mail server with a more detailed explanation. It's an annoying occurrence in email sending. As common as they may be, senders go nuts over email bounces.

It ain’t pretty.

While we’ve spoken before on how your email bounces are less important if you focus more on deliverability, it’s a hard problem to solve. Largely due to the fact that in some cases, a bounce really is a technical error that can be remedied with some due diligence. Still, with a quick fix, your bounces should go down, right? 

That depends on what kind of bounce you’re getting.

Hard Bounces versus Soft Bounces

Email bounces (which make up part of your total delivery) occur when an email is undeliverable in some way, and you will usually receive an auto-reply to your message as to why it could not be delivered. There are two types of bounces you can run into when sending email — hard bounces and soft bounces.

Hard Bounces

Hard bounces, also known as permanent failures, mean that the message couldn’t be delivered due to some sort of invalid, unchangeable, permanent reasons. Good examples of hard bounces are invalid addresses, the email server no longer exists, misspelled domain names, etc. Nothing you do will change this bounce, so it’s best to just throw those emails off your list.

Most ESPs (Mailgun included) will stop attempting to send the message after the first attempt. If it has nowhere to go, you can’t deliver it.

Soft Bounces

On the other hand, soft bounces (temporary failures) are unable to be delivered due to some kind of temporary circumstance. What kind of temporary circumstance? Anything from the email message being too large to the recipient’s mail server being down. 

There isn’t any one solution for soft bounces, but the email still can’t be delivered to the receiving server at that point in time. In these cases, most ESPs will attempt delivery a few more times in case circumstances change, and then stop after several tries.

What about a sudden increase in email bounces?

When it comes to hard bounces, you shouldn’t see a sudden increase. If you are sending to a list for the first time without validating first, you might see a larger hard bounce rate due to factors like typos. As we stated earlier, just remove those addresses from the list to bring your hard bounces down.

To avoid them entirely, you can validate an existing list or add on a validation service to your forms to correct users ahead of time or if they make a typo, giving you a cleaner mailing list from the start.

Soft bounces are complicated

Soft bounces are a little different in that there isn’t some one-size-fits-all solution for them.

Some soft bounces have easy solutions, like removing a bit of the content from an email that’s too large. For others, it can get a little complicated. 

Some senders might want to continue to send to inboxes that are full under the assumption that those inboxes will eventually be cleaned by the recipient in order to free up space for more emails. However, chances are that the recipient’s inbox is full because they’ve abandoned it. Full inboxes are usually a telltale sign of an older email list and should be treated as an invalid email and cleaned from the list entirely.

There is also the chance that you’re getting a higher soft bounce rate because your email service provider has placed limits on your account.

Well, this is awkward.

Wait, what?

Yes, ESPs will limit how much damage you do to your reputation, and this can be reflected in your soft bounces. Before you bring out your torches and pitchforks — hear us out.

Chances are if you’re experiencing soft bounces in this way, it’s for your own good. Usually, there is something you are doing that would adversely affect your reputation or others if you’re on a shared IP. Allowing risky sending to continue from a shared sending IP hurts well-meaning senders, and an ESP needs to take care of every sender — including careless ones.

There are other cases beyond soft bounces in which you can find yourself limited to send. Sending too many messages at one time without a proper warm-up, hitting spam filters with risky sending practices, or recipients that did not consent to your email messages and complain are a few examples of factors that affect your sending limits, too.

What you can do about a sudden increase in soft bounces?

If you find yourself in this situation, the first thing you should look at is your list. How old is it? How were these contacts obtained? When was the last time it was cleaned? Cleaning it up should be your top priority. Sending to engaged, consenting users alongside well constructed, relevant messages is the best way to improve your reputation and get out of soft bounce purgatory. 

There are cases where you’ve got a clean list, you’ve properly warmed up your dedicated IP address, and your users actively engage with your emails; yet somehow you end up getting hit with account limitations or soft bounces. It is possible for the ESP to make a mistake and misclassify your domain or IP address as risky, in which case your ESP will have a recovery process in place to solve it. 

Email bounces are a symptom

We emphasized this a lot when we talked about bounce rates, but we’ll reiterate here — the problem isn’t your bounces, it’s what’s causing them in the first place. Bounces are almost always a symptom of out-of-date or poor sending practices, and that means poor deliverability. If you're currently trying to do some technical problem solving with email bounces, we have the documentation for you!

You could have an amazing email marketing campaign, but that means nothing if you aren’t landing in the inbox. Focusing more on making sure that your sending habits fit with healthy email deliverability will take care of your bounces as well as keep you from being limited by your ESP in the future.

Last updated on August 28, 2020

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