but then, why not a scheme such as
user+tagstuff(_at_)domain
(replace '+' with any char(s) you prefer). this would make it almost trivial
to implement in MTAs that support address extensions.
Because it would collide with the way that address extensions are used
now.
BATV is handled in the MTA at SMTP time, but address extensions are
handled at delivery time or later. If the BATV stuff were put in an
extension, you couldn't tell it from VERP and other delivery time
extension usages.
Also, whatever the scheme is, there is another class of applications to think
of. these are applications that use the sender address as an element to
determine the "reputation" of a transaction (spamassassin AWL for instance).
such apps should be made aware of the various BATV styles.
See subsequent message.
Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
"I dropped the toothpaste", said Tom, crestfallenly.