Why Emails Bounce?

Email message rejected by a recipient's mail server. Email message has not been delivered. Non-delivery status failure.

Jelena avatar
Written by Jelena
Updated over a week ago


Emails bounce all the time.
It sounds scary, but as long as you’re keeping your bounce rate under control, and clean up those bounced email addresses when necessary, your bounce rate won’t have a negative impact on your email account delivery rate.
Autoklose has a way of handling bounces internally, you can read more about it here.  

Why email bounces?

An email bounce is an error message you get when the email you’ve sent isn’t delivered. Your email server or the destination email server sends this Non-Delivery Report (NDR).
A contact is marked as bounced when their receiving email server rejects an email campaign or automation email.

There are a lot of reasons that can cause an email to bounce, and this article will cover most of them. 

  1. Mailbox is full- This is pretty self-explanatory. If your recipients have too many emails in their Inbox folders, your email will bounce back until there’s enough space for your email. 

  2. Recipient’s server is down - When the server has crashed or is overloaded/under maintenance, it’s unreachable, and it is impossible to deliver to it. 

  3. Email is too big and content-heavy - If your email is too big and packed with a lot of images or huge attachments, that might be a reason for a bounce report. 

  4. Autoresponder - This is the least likely scenario, but sometimes when recipients are on vacation and OOO replies are turned on, your email could bounce back but the message will land in their inbox as soon as the autoresponder is turned off.

  5. Bad/ Incorrect/ Fake email address - If your contact changed the company or is no longer using that email address/ there’s been typo a while entering the email address/ or in the worst-case scenario, your contact gave you a fake email address out of concern for spam - no matter what the reason is, invalid email addresses are the most common reason for bounces. 

  6. Blocked email - This is often the case among government institutions or schools, where servers can have stricter spam filters when it comes to receiving emails. Mail servers can also block your email if the “From” address does not match the account on the email server.

  7. The recipient may have blocked your email address on purpose - Recipients can block the senders they don’t want to hear from again. In that case, your emails will bounce even if they came through in the past. 

  8. The sending IP address or email domain you are using have been blocked- If you find yourself on a blacklist, it might mean you are suspected of spamming or email fraud or your domain has a bad reputation. 

How to know exactly why your email bounced?

When an email bounces, your email server or the destination email server sends a Non-Delivery Report. Those often include code numbers and messages to explain those codes. We have compiled a list of bounced codes and explanations for each code. 

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