On Wed, 2004-12-08 at 11:20, David Woodhouse wrote:
On Wed, 2004-12-08 at 18:47 +0000, John Levine wrote:
I do agree that bounces vs. rejects are an increasing problem, and
I'm having trouble figuring out if there's any way I can do bounces
reasonably for the fraction of the mail here for which I can't tell
if it's deliverable at SMTP time.
The only real answer I've found is to make sure that during _normal_
operation, there isn't actually any mail in that category ("can't tell
if it's deliverable at SMTP time").
I do recipient verification callouts (with caching, of course) for the
domains for which I am MX backup (and in some cases, also for mail I'm
forwarding). Obviously it's pointless being an MX backup unless you
actually accept the mail while the primary is down; but that's not
normal operation.
The spammer often ignores MX priorities specifically to discover SMTP
servers that accept mail for a particular domain without respect to
valid users. There is still an advantage using BATV even in the case
where there is a bounce generated in this scenario. The receiving MTA,
if using BATV, should be able to reject a bounce when the MAILFROM is
NULL. This is the reason for BATV.
It seems the proper etiquette for a bounce would be to ensure a NULL
MAILFROM when issuing a bounce. This behavior should include virus
detection, vacation notices, and other message related events generated
as a result of a message being rejected and returned. Unfortunately,
the setting of MAILFROM for a bounce is optional. : (
-Doug