Is there a solution for 550 User Unknown mails

[Sahil Tandon]

Derrick Ryalls wrote:

> This is perhaps off topic, but all machines in question are running 
> FreeBSD  :)

This problem is related to the configuration of your MTA, not FreeBSD.

> Every day I get dozens of failed email notifications in the form of:
> 
> UNDELIVERABLE MAIL Your message to the following recipients cannot be
> delivered: <wtcxqomfaq at alicedsl.de>: webmail.hansenet.de
> [213.191.73.2]:
> 
>            RCPT TO:<wtcxqomfaq at alicedsl.de>
> 
> <<< 550 RCPT TO:<wtcxqomfaq at alicedsl.de> User unknown

[...]

> With secondary mail servers, I am accepting mail for other domains,
> and then forwarding them on.  It is my belief that acting as a
> secondary mail server is what is causing me to receive all these
> errors.

[...]

> Assuming that my guessing is correct, is there any way to stop this
> flood of reject emails short of not being a secondary server for
> anyone?

Which MTA?  In Postfix, you can use the relay_recipient_maps parameter 
to query a list of valid recipients.  The MX for which you're acting as 
secondary should be able to provide the list.

--
Sahil Tandon <sahil at tandon.net>