While working on a particular problem, I noticed in the documentation that local delivery routers (by default, but changeable) do not deal with multiple domain recipients in the same envelope. I wondered what would actually happen in the unlikely even that that occured, and found out that any e-mails to additional domains in the same envelope simply disappear, even though they appear to be delivered to the sending MTA. Even though the occurence of this happening in the wild approaches zero, I wrote a little acl to drop anybody attempting it since likely only faulty MTA's (spammers) would even attempt it. Here it is for anybody that cares (and maybe somebody has a better idea to accomplish the same thing)
# Disallow multiple domains in the same envelope
warn set acl_m9 = $acl_m8
set acl_m8 = $domain
drop condition = ${if eq{$acl_m9}{$acl_m8}{0}{1}}
condition = ${if eq{$acl_m9}{}{0}{1}}
message = This SMTP server does not accept multiple domains in the same envelope
Kelley
