suggestions for altering outbound SMTP to work-around multi-CC denials

Recently, mail to recepients at several domains (gmail.com, verizon.net) i=
s being refused when multiple receipients are CC'ed (even when
only a small number -- 2, 3 -- of people are CC'ed). This behavior is repe=
atable and consistent, not transient failures.

I'm considering ways to work around this by programmatically altering some=
 outbound mail.

I'm looking for suggestions (within or outside NMH) for steps 2a & 3 of th=
e proposed workflow:

	1. compose mail normally (multiple To: & CC: body headers)

	2. normal MUA (nmh or claws-mail) prepares outbound mail as usual, includ=
ing creating a single Fcc copy per-outbound message, with
	   all recipients included,

	2a MUA hands the message off to "something" as if it is passing it to the=
 local MTA (postix), but
	   actually hands it to a filter

	3. [some process] filters the outbound mail:
		if [ destination =3D~ *@(gmail.com|verizon.net) && ( # of recipients > 1=
) ] =

		then
			initiate a separate SMTP connection for each recipient, where the messa=
ge
			body is altered to remove the multiple To: and CC: lines (leaving just =
the
			recipient used in the SMTP envelope "To" line)
		else
			deliver unaltered message via SMTP
		fi


I don't know if this can be done natively with nmh tools, some wrapper
around send(1) or post(1), or using sendmail/pipe in /etc/nmh/mts to
call a filter (ie., /usr/local/sendmail) to do the rewriting and then
pass the messages off to an SMTP daemon (postfix) on localhost or some
other mechanism.

I'm already using postfix for things like routing outbound email to
different proxies based on the sender domain, and maybe this task
could be done from filters called by postix.

Ideas, and has anyone else started seeing this problem (enterprise SMTP se=
rvers refusing to accept mail that references multiple
recipients in message body)?

Thanks,

Mark

-- =

Mark Bergman    Biker, Rock Climber, SCUBA Diver, Unix mechanic, IATSE #1 =
Stagehand
'94 Yamaha GTS1000A^1					   2023 Triumph GT Explorer
	  		https://www.flickr.com/photos/rmsppu