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Email delivery

Pay close attention to bounces

Shane Rice Shane Rice

Many factors influence email delivery for your domain. The content of each message is important but equally as important is how people engage with email from your domain. A key signal for your domain's engagement is your bounce rate. Most inbox providers interpret a high bounce rate from a domain as low-quality sending behavior. No one can engage with an email that bounces, and it makes sense they would see bounces as a key factor in a domain’s sending reputation. If someone buys a list from a 3rd party, has a service that’s prone to abuse, or low-quality registrations, they’re going to generate a lot of bounces. And that can hurt your sending reputation.

Not every email bounce is the same #

There are two primary types of bounces, hard and soft. It's important to understand the differences between each type.

A soft bounce happens when an email can’t be delivered for a temporary period of time. Soft bounces include instances where a mailbox is full, or when there’s an auto-responder set to bounce messages for a short period. Other soft bounces include DNS errors or system capacity issues where a mail server’s queue refuses to accept any more message. It’s important to monitor soft bounces because enough of these over time can have an impact on your domain’s reputation.

Hard bounces happen when an email address doesn’t exist or when there are fundamental problems with a receiving mail server. Typos are the most common cause of hard bounces. When a message hard bounces on Postmark, we flag it to prevent sending in the future. We’ll cover more of the specifics of exactly how this works later in this post.

And then there are spam complaints. Technically, these aren’t bounces because someone has received your message and taken the time to tell their inbox provider it was spam. Even though this isn’t a bounce in the classic sense, your ESP will treat it the same as a hard bounce to prevent delivery problems for you and their other customers.

How Postmark handles bounces #

Whenever Postmark receives a hard bounce notification from a mail server, Postmark suspends future delivery to that address automatically, and it can optionally notify your application of the bounce via our bounce webhook. With this webhook, you can take appropriate actions on your end to avoid sending to that address, whether that’s reactivating the address once it's available again, fixing a typo, or notifying an account holder there’s an issue with their email address.

We also suspend delivery whenever Postmark receives a spam complaint, but you can't reactivate addresses with spam complaints without contacting Postmark support.

Since Postmark automatically deactivates delivery for addresses with hard bounces and spam complaints, you’ll want to take actions on your end to help users resolve the issues. Soft bounces are little different, in that we don't automatically take any action for future email. This isn't normally an issue because soft bounces resolve themselves relatively fast. You also won't need to worry about having to reactivate addresses for soft bounces.

Best bounce handling practices for your app #

When your app has a user whose email address has been deactivated, you should try to engage with them to see if you can update their email address. Chris Nagele wrote about how we handle bounces with Beanstalk while using Postmark, and Sifter showed how they use bounce data from Postmark in a similar way . A few things you can try to re-engage with them include…

  • display a message to the user the next time they log in
  • notify administrators or account holders of the problem
  • deactivate email notifications for that user to save resources
  • notify the user at a backup email address if you have one on file

Email verification is a good way to avoid sending bounces to email addresses with a typo. Although, you should keep a close eye on email verification email stats to make sure you aren’t solving one problem but adding another. If someone were to start spamming your sign up form with email addresses to trigger a verification, many of those addresses could bounce and start having an impact on your delivery. An easy way to track email verifications is tagging your email verification messages with your ESP to keep track of how they’re performing. You can tag messages by type with Postmark when you send via SMTP or our API.

If you have a service with inherent problems with bounces, you might even try an email verification service like the ones below to reduce the number of garbage emails entered in your application.

Bounces happen, the key thing is how they impact your domain’s reputation. Domains with enough volume can keep track of engagement with postmaster tools, and every ESP can help you manage your bounces. A little bit of planning and prevention will go a long way towards protecting your domain’s reputation.

Shane Rice

Shane Rice