No such statement, BUT you should do some heuristic analysis.  Do a
search of the last months archive e.g.,

S * IN listname SINCE JUNE TO JUNE

(you'll probably need to "wrap" that in "job" language for the release
that you're running)

Find the line length of what is probably the largest legit.
NON-attachment (and probably non-HTML) posting; call that value
'hi-watermark.'  Add or update the following list keyword definition:

* SIZELIM= hi-watermark

This will no doubt cause certain posters a problem from time to time
since they might have a legit posting that exceeds that value, esp. when
you take into account mail headers, HTML encoding,   Some users will be
able to figure out how to cut out excess text incl. HTML as well as
quoting previous material.

Alternatively, set the recalitrant posters to REVIEW.

Update your WELCOME file as appropriate.

Announce such change to the membership.

Good Luck.

/Pete Weiss