Email bounces: What to do about them

Email bounces occur when an email cannot be delivered to a recipient’s inbox, but soft and hard bounces come with very different set of challenges.



Email bounces — the pesky phenomenon that happens when email messages cannot be delivered to a recipient’s email address. They can be a source of much grief – blood, sweat, tears, curses… high email bounce rates can definitely throw off your groove.

There are many different possibilities for an email bouncing. As a result, a "return to sender" message (also known as an SMTP Reply) is applied and sent from the recipient's mail server with a more detailed explanation for the bounce back. It's an annoying occurrence in email delivery. But, as common as they may be, senders still go nuts over bounced emails.

 Why are bounces such a hard problem to solve? This is largely due to the fact that, in some cases, a bounced email address really is a technical error that can be remedied with some due diligence. Still, with a quick fix, your bounces should go down, right? 

Well, that depends on what type of email bounces you’re getting.

Hard bounces versus soft bounces

Email bounces (which make up part of your total delivery) occur when an email cannot be delivered to a recipient’s inbox. You will usually receive an auto-reply to your message that gives you a reason for the non-delivery. 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 is undeliverable due to some sort of unchangeable, permanent reason. Common reasons for hard bounces are invalid email addresses, the receiving server no longer exists, misspelled domain names or recipient addresses, etc. Most email providers – Mailgun included – will stop attempting to send hard bounce messages after the first attempt. If it has nowhere to go, not even we can deliver it.

A common misconception is that nothing you do will change this bounce, so some senders think it’s best to just throw those email addresses off your lists or CRM. Deleting customer data is not recommended. Instead, emails that hard bounce should be added to a suppression list (Mailgun does this automatically)

Consider this scenario: your customer changes ISP from Yahoo to Gmail and forgets to update their email account on your system. Suddenly, you receive a hard bounce from this email address. The customer still wants to hear from you, so deleting their record would mean losing a customer. Instead, we use this hard bounce as a reminder to prompt them to update their valid email address another way, either in-app or using a CPaaS method.

Soft bounces

On the other hand, soft bounces (temporary failures) cannot be delivered due to some kind of temporary issue. What kind of temporary circumstance? Anything from the email message being too large to the recipient’s email server being down. 

There isn’t any one solution for soft bounces, but the email still can’t be delivered to the recipient’s mailbox at that point in time. In these cases, most ESPs will attempt delivery a few more times in case circumstances change and then stop if the email continues to bounce.

Bounced back emails are just one of many possible outcomes when sending an email – read our ultimate guide to email metrics to better understand your email stats. 

What about a sudden increase in email bounces?

When it comes to hard bounces, you shouldn’t see a sudden increase at any point while sending emails. If you are sending to a list for the first time without validating it first, you might see a larger hard bounce rate due to factors like typos. As we stated earlier, just add those addresses to a suppression list to bring your hard bounces down. It’s as easy as that, with (hopefully) no profanity involved.

To avoid them entirely, you can verify an existing list or add a double opt-in feature to your forms to ensure users’ emails are correct. This cuts down on wrong addresses, giving you a cleaner mailing list from the start and a better sender reputation.

Understanding soft bounce situations

Soft bounces are a little different from hard bounces 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 sending to inboxes that are full under the assumption that the recipient will eventually clean those inboxes to free up space for more emails. However, the chances are that the recipient’s mailbox is full because they’ve abandoned it like an old Blockbuster Video. Full inboxes are usually a telltale sign of an older email list and should be treated as an invalid email and sent to a suppression list.

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

Wait, can my ESP place limits on my account?

Yes, ESPs will limit how much damage you can do to your reputation, and this is 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 may not necessarily be a bad thing. 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 other well-meaning senders, and an ESP needs to take care of every sender.

There are other cases beyond soft bounces where you can find yourself limited while sending. 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 can you 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 well constructed and relevant messages to engaged, consenting users is the best way to improve your reputation and get out of soft bounce purgatory and into delivery heaven. 

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. 

Want to know more about email best practices? Check out our Email Growth Playbook, a database of 60+ tactics to help you increase the performance of your email campaigns.

Email bounces can be solved

We emphasize this a lot when we talk 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. Focus on healthy deliverability sending habits and the bounces will take care of themself, and keep you from being limited by your ESP in the future. So follow best practices, keep grooving, and the bounces will take care of themself.

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