Hmmm...this looks very much like the [unhelpful] message GMail gives when you try to post to a group that you aren't subscribed to. In fact I just posted to your group using my GMail account, knowing that I was not a subscriber; and I got exactly the same message back.
If you continue to page down, the actual reason for rejection will probably say something like this:
The response from the remote server was:
510 5.1.1 Your email address,?noname@..., is not subscribed to that group. To subscribe, send an email to?[email protected], or visit?/g/WMRHSMG/join
If you know for a fact that the person is indeed subscribed to the group, then he's probably trying to post with an alternate email address. Look up his record in the Member's List and tell him what email address he should be using. If you can't find his subscriber record, send him an invitation.
Hope this helps,
Bruce
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The system Help is your friend.??
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