[SOLVED] Undelivered Mail Returned to Sender

[admin1]

A large number of email messages (NOT enough to affect the server's performance but enough to be a major pain) with the subject

Undelivered Mail Returned to Sender

followed by:

This is the mail system at host server.domain.com.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<jsmithnn@domain.com>: domain.com

The recurring pattern is a legitimate email account with 2 or 3 letters added to the UID part or the email address (jsmithnn@domain.com).
Is this an attack on the server (spam or otherwise)
or something else?

Thanks

[bdial]

google for 'backscatter spam' and you'll find manu an explanation for this probably.

[admin1]

Thank you, bdial, for your response.
Is there any way to set Zimbra to automatically reject mail that is sent to nonexistent users?
Are there any Zimbra solutions to 'backscatter spam'?

[Baylink]

What you don't say is *who's getting the messages*.

The problem with backscatter is that it's responses to forged messages in the names of *valid* mailboxes, otherwise it wouldn't get there at all.

About the only rational thing to do these days, is to drop any incoming bounces on the floor -- your users' outgoing mail should generate any necessary bounces *inside your mail system*.

But yes, google; there's lots out there on backscatter and outscatter.