Bounce, return email from mail server

What is a Bounce Email?

Definition: A bounce email is an email that has not been delivered to its recipient. It is sent back to the sender with an error message.

Bounces are undeliverable emails sent by mail servers. They are not spam, since they are theoretically legitimate. However, given that many spammers impersonate legitimate individuals, some bounces may reach you even though you did not send the original email. This can pollute your inbox. On the other hand, in normal circumstances there is little reason to receive Bounces when you use the same mail server for sending and receiving emails, because in the event of a delivery error, the information message is distributed directly locally (unless the recipient’s server is not correctly configured).

Glossaire Définition Bounce

What is the content of a Bounce notification message?

The content of a Bounce notification message varies depending on the type of Bounce and the mail server. In general, the message contains information about the recipient, the reason for the bounce, the error code, the IP address of the mail server, etc.

What types of bounce are there?

There are two types of bounce: hard bounce and soft bounce. A hard bounce is definitive and means that the email can never be delivered. Soft Bounce is temporary and means that the email could not be delivered for the moment, but can be retried later.

How does the Bounce Rate affect deliverability?

A high Bounce Rate can have a negative impact on email deliverability. Email providers may consider emails with a high Bounce Rate as spam and place them in spam folders or block them completely. It is therefore important to maintain a low bounce rate to improve email deliverability.


Example of a Bounce message. The subject of the return mail is: “Undelivered Mail Returned to Sender” and the content begins as follows: “This is the mail system at host I am sorry to inform you that your message could not be delivered to one or more recipients. It is attached below (…)”.

Exemple de bounce


Recognising a bounce is very simple, because it is very often sent by postmaster, or [null] and contains a subject and content that are easily identifiable. On the other hand, it is extremely complex to know whether or not the bounce originates from spam. By default, ALTOSPAM detects whether the bounce is spam and blocks it. However, the administrator has the option of letting all bounces through or blocking them all.

Additional information

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