[Mailman-Users] Can Someone Explain This?

[sherwin]

I am recently having trouble posting messages to Ibiblio from my
AT&T mail account.  There have been issues lately with AOL and
Yahoo changing their headers, but I was not affected by this.

My email postings to Ibiblio are being rejected with the following error:

This is the mail system at host lists.ibiblio.org.

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

<midfex at lists.ibiblio.org>: Command died with status 2:
     "/usr/lib/mailman/mail/mailman post midfex". 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'.



Reporting-MTA: dns; lists.ibiblio.org
X-Postfix-Queue-ID: 0CFE6235EE
X-Postfix-Sender: rfc822;sherwindu at att.net
Arrival-Date: Fri,  9 May 2014 02:48:43 -0400 (EDT)

Final-Recipient: rfc822;midfex at lists.ibiblio.org
Action: failed
Status: 5.3.0
Diagnostic-Code: x-unix; 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'.


How can this be fixed?

                   Sherwin Dubren