Mailing Lists rejecting googlemail users

[#1]

Good afternoon
I originally had problems with googlemail users not being able to subscribe to my Mailing List and I think it was Bob who pointed out that sometimes the automated reply went into the Spam folder. This resolved the issues but we are now having further problems when googlemail users try to subscribe.
The initial automated reply is being received but when users try to confirm by replying the second e-mail is rejected with the message below. 
Delivery to the following recipient failed permanently:
    council-sc.1229356674.deoficloipmjbicojeio-turnbull.jon=googlemail.com@redmarshall.plus.com
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 #5.1.0 Address rejected council-sc.1229356674.deoficloipmjbicojeio-turnbull.jon=googlemail.com@redmarshall.plus.com (state 14).
Please can anyone suggest what we are doing wrong?
many thanks
John

[#2]

http://community.plus.net/forum/index.php/topic,71307.0.html
Have you got the catch all turned on?

[#3]

Thanks Bright Spark.
I haven't got catch all switched on but having read the link you attached it seems I might as well forget about Mailing Lists.
It is a pity because we have found them useful for keeping our community group in touch as all subscribers can contact everyone else. In the My Circular system it seems only the owner (me) can send out information.
Another good idea down the drain!
once again thanks for your help
  John