Eric Thomas's description rang a bell or two for me.

>      HTML does tend to have a lot of periods, but there
> are no leading periods anywhere in the message and there should be no
> double-period issue.

I had one contributor who was using a double-layered stack of
quoted-printable processors, which had the effect of breaking a line twice:
the trouble occurred when the first break occurred just after a period,
which the second break then isolated on a single line.

>  Without a wire trace, it is not possible to know for
> sure what has happened.

What we managed to do, instead, was to get the original message and
determine what would have come next after the truncation. (In fact, I had
him copying me directly on items sent to the list, so I could compare.)

In his case, one of the half-dozen internal hops between his email and his
company's domain border was not performing the SMTP-mandated transparency
operation on leading periods. (We proved that the same thing happened on
inbound email; I sent a test message with a line consisting of a single
period, and the portion following it was dropped.)

You may be right; your truncation may have nothing to do with the SMTP
end-of-message flag. But that case can happen with periods nowhere near the
beginning of the line, and it would certainly be worth establishing whether
the same mail truncated when it goes through the list is also truncated when
sent directly.

I get lots of people complaining about the list when their own email service
is at fault.

Hal Keen