The Most Common Bounce Notifications and Their Meanings

When sending an email to a recipient, it may happen that the receiving server doesn’t accept your email. The email can’t be delivered and bounces.  

The receiving server reports back to our system that your email couldn’t be delivered. The causes for bounces can be versatile.

In general, each server can send completely individual bounce messages. There is no standard.  

The following overview is a list of the most common bounce feedbacks that reach us:

Wrong Address

host is unknown / host not found
invalid adress / invalid recipient
mailbox not found / mailbox is unavailable
no mailbox here by that time
no such user
recipient e-mail adress unknown
user unknown / unknown user
said: 550

Filtering by Receiving Server

mail was identified as spam
only registered users may use this system
recipient address rejected
relay not permitted

Receiving Server Hardware Problems

error writing message
message could not be stored
relay access denied

Inbox problems

mailbox does not exist
mailbox has been deactivated / disabled / discontinued
mailbox is full
mailbox unavailable
user has exhausted allowed storage space

The notifications said: 550 and said: 553 are often used by servers to indicate a spam classification.

Please note: We recommend implementing the steps from this help center post to optimize the deliverability of your newsletter.

Help & Support

If you have any questions or need further assistance, please contact our service team at any time.