If an email is marked as ‘undeliverable,’ it means it did not make it to the inbox of the recipient, due to one of a variety of reasons. Invalid email addresses, mail server blocks, marking a message as spam or unsubscribing, a full inbox - any of these events can cause an email to be undeliverable (see detailed information about bounces below).

What is a bounce?

A bounce occurs when your email went to a specific address, but the mail server for that address sent it back saying it was ‘undeliverable.’ There are many reasons for this:

  • A soft bounce happens when the recipient’s address is correct, but the email was still returned by the server before it reached the recipient. A full inbox, a server that’s down, a message that’s too large, or even an auto-reply can all cause a soft bounce.
  • A hard bounce happens when your email is considered permanently undeliverable because there was either a problem with the recipient’s address – such as a typo or a change of domain name – or the recipient unsubscribed or marked your message as spam at one point. The system will attempt to resend a deferred email for up to 72 hours from the first attempt. If the deferred email is still undeliverable at this time, the email address is marked as undelivered and placed on the bounce list.

PLEASE NOTE: Hard bounce emails are automatically forwarded to our Media research team for them to be updated.

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