John Klensin has an internet-draft out that addresses this issue. See
section 3 of draft-klensin-name-filters-02.txt. I don't know if this will
be any more useful than RFC 2822 when it comes to bashing the clueless over
the head, but every bit helps, I guess.
Unfortunately I'd have to say NetSol is not alone on this as a
vast majority of the sites I've had to enter an email address will not
accept a user+detail@domain format... I find it to be quite annoying
that I can use the format as it helps with filtering of email and is
completely valid according to the current RFCs wrt mail.