[ Apologies if this is a duplicate -- I wasn't on the list
when I posted it earlier, and I think the first copy has
been swallowed.... ]
I want to write a recipient ACL in which a callout is made
to test the deliverability of the recipient address and,
(a) if the recipient is definitely deliverable, the ACL
returns `defer';
(b) if the recipient is definitely undeliverable, the ACL
returns `deny'; and
(c) otherwise it returns `accept'.
(The application is for a secondary MX host where it is
not practical to apply the same content filtering etc.
conditions as on the primary; therefore, in the most
common case where the primary is up -- and therefore the
recipient test succeeds -- I want to return 451; if the
address would in any case be undeliverable, 550; and
otherwise accept the mail.)
So, I tried something like this:
defer domains = +relay_domains
verify = recipient/callout,nocache
message = Primary MX for $domain is up, please try that
deny domains = +relay_domains
!verify = recipient/callout
message = Recipient $local_part@$domain not deliverable
accept domains = +relay_to_domains
... and in the first two cases it works. Unfortunately, in
case (c), where the remote host is down, the defer
condition is failed and returns ``451 Could not complete
recipient verify callout''. My reading of the spec
(§39.32) is that this is the design behaviour: verify =
recipient/callout conditions are special in that a defer
result will immediately cause the whole ACL to defer.
The defer_ok modifier doesn't help in this case as it
causes the condition to return true, which would mean that
the `defer' stanza fires when the remote host is *down*,
which is exactly wrong.
What I'd like in this case is for the verify = recpient
condition to result in a failure with an appropriate value
in $recipient_verify_failure or somewhere else that I can
test it. Is there a way to do this?
(I actually have an interim solution to this which uses
perl to perform the callout, but that's horrid -- one
implementation of SMTP per program is enough....)
--
``The efficiency of the rocket launcher team was also very impaired.''
(commentary on film of British troops given LSD as part of a 1960s
chemical warfare experiment)
