Mailman and Postfix not sending mail

[swanny]

Hey everyone,

I created a mailing list with Mailman. It has around 3800 entries and it's crucial that I get this working ASAP, but I'm new to the world of linux and it's slightly frustrating.

I added the aliases Mailman gave me to my /etc/aliases file, ran 'newaliases' and it was all fine. All of the other aliases work and send mail properly, but when mail is sent to this new list@domain.ca, it returns this error:

This is the Postfix program at host mail.xx@xx.ca.

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 Postfix program

<xx@xx.ca>: Command died with status 2:
"/usr/local/mailman/mail/mailman post engglink". Command output: Group
mismatch error. Mailman expected the mail wrapper script to be executed as
group "mailman", but the system's mail server executed the mail script as
group "nobody". Try tweaking the mail server to run the script as group
"mailman", or re-run configure, providing the command line option
`--with-mail-gid=nobody'.

Final-Recipient: rfc822; engglink@xx.ca
Action: failed
Status: 5.0.0
Diagnostic-Code: X-Postfix; Command died with status 2:
"/usr/local/mailman/mail/mailman post engglink". Command output: Group
mismatch error. Mailman expected the mail wrapper script to be executed as
group "mailman", but the system's mail server executed the mail script as
group "nobody". Try tweaking the mail server to run the script as group
"mailman", or re-run configure, providing the command line option
`--with-mail-gid=nobody'.

Can anyone shoot me in the right direction? It's a mailing list for my university, so I really need it to be working.

[HROAdmin26]

Google "Try tweaking the mail server to run the script as group" => This and This