David Lee wrote:

> Anyone on thoughts on what follows? Thanks in advance.

[Different MaxMessageSize for different users]

You could set MaxMessageSize very high, and then use a milter
to reject oversized messages based on sender/recipient combination.
The milter can reject at the MAIL FROM: stage (if the SIZE=xxx ESMTP
parameter is given) or after DATA (trickier if you have multiple
recipients.)

Regards,

David.