> I got a message from one of my list owners that he had received an error report
> as below:
>
> The enclosed message, found in the #######-L mailbox and shown under the spool
> ID #### in the system log, has been identified as a possible delivery error
> notice for the following reason: "Sender:", "From:", or "Reply-To:" field
> pointing to the list has been found in mail body.
>
> The subscriber who sent in the message uses cc:Mail. cc:Mail has a tendency to
> identify different replies within a message by use of a simple boundary.....
>
> What I am wondering is why Listserv even checks the body of the message for
> such content words.... or is it perhaps that there may be a problem between
> Listserv and cc:Mail and interpretation of these simple boundary reply
> separators. Perhaps Listserv is interpreting them as a separate message within
> the body itself...

It's one of LISTSERV's methods for preventing mail loops.  There are broken
mail servers that return error messages to the list, instead of where they
should go.  If one of those messages gets through to the list, it is likely
to cause a loop.

It's best to advise your subscribers to delete the old headers from replies.
It's a good habit to get into anyway, as many people are annoyed by a lot
extraneous material in posts.

However, if it's really necessary and you feel it is safe to do so, the
check can be disabled with Loopcheck=Nobody.