[Mailman-Developers] Adding unrecognised bounce formats?

[Colin Mackinlay]

How easy is it to add a new bounce format?

My SMTP server sends all mai through the messagelabs virus scan 
servers and 550 bounces for unrecognised addresses typically come 
back in the format:

This is the mail delivery agent at messagelabs.com.
I was not able to deliver your message to the following addresses.

<xyz at hotmail.com>:
65.54.166.230 does not like recipient.
Remote host said: 550 Requested action not taken: mailbox unavailable

Everytime a mailing or membership reminder goes out I get stacks of these!

If someone can point me in the right direction with a few clues I can
probably figure out what to do.

Thanks

Colin