reject_unverified_recipient applied to virtual alias destination

[Jesse Norell]

Hello,

  I am trying to utilize 'reject_unverified_recipient' selectively, so
that only addresses for domains which I host are verified, ahead of
permitting sasl senders, in order to avoid bounces for unknown
recipients of local domains.  In summary, the setup seems to work
correctly for mailboxes, but a problem arises with forwarded addresses,
where verification is performed for the destination of the forward
(external domain), rather than the smtp recipient address (local
domain).

  I am using postfix 3.4.14-0+deb10u1 from Debian.

  I setup test.com to demonstrate and created a mail...@test.com mailbo
x and a forw...@test.com forward to my gmail account:

   # postconf virtual_mailbox_domains virtual_mailbox_maps
   virtual_mailbox_domains = proxy:mysql:/etc/postfix/mysql-virtual_domains.cf
   virtual_mailbox_maps = proxy:mysql:/etc/postfix/mysql-virtual_mailboxes.cf

   # postmap -q test.com mysql:/etc/postfix/mysql-virtual_domains.cf
   test.com

   # postmap -q mail...@test.com mysql:/etc/postfix/mysql-virtual_mailboxes.cf
   test.com/mailbox/

   # postmap -q forw...@test.com mysql:/etc/postfix/mysql-virtual_mailboxes.cf
   m...@gmail.com


I set 'reject_unverified_recipient' via the mysql-virtual_recipient.cf map:

   smtpd_recipient_restrictions = permit_mynetworks,
     reject_unknown_recipient_domain,
     reject_unlisted_recipient,
     check_recipient_access 
proxy:mysql:/etc/postfix/mysql-verify_recipients.cf, 
     permit_sasl_authenticated, 
     reject_non_fqdn_recipient,
     reject_unauth_destination,
     check_recipient_access proxy:mysql:/etc/postfix/mysql-virtual_recipient.cf,
     check_recipient_access mysql:/etc/postfix/mysql-virtual_policy_greylist.cf,
     check_policy_service unix:private/quota-status

   # grep query /etc/postfix/mysql-verify_recipients.cf
   query = SELECT 'reject_unverified_recipient' FROM mail_domain WHERE domain = 
'%s' AND active = 'y' AND server_id = 1


The mysql-verify_recipients.cf query works correctly to for domains I
host and for external domains:

   # postmap -q test.com mysql:/etc/postfix/mysql-verify_recipients.cf
   reject_unverified_recipient
   # postmap -q gmail.com mysql:/etc/postfix/mysql-verify_recipients.cf
   #    (<-- no output)


  What I expect and want is that lookups for test.com recipient
addresses will undergo address verification, and addresses for external
domains like gmail.com will not.  However when send to
forw...@test.com, what happens is address verification for m...@gmail.com
 fails.  The failure is correct, because my test server does not have
outbound smtp access (nor ipv6), but I don't want address verification
for the gmail.com address to take place at all.

Replies from my smtp conversations are:

   Rcpt To:<mail...@test.com>
   250 2.1.5 Ok

and on first attempt: 

   Rcpt To:<forw...@test.com>
   450 4.1.1 <forw...@test.com>: Recipient address rejected: unverified 
address: Address verification in progress

   then on subsequent attempts with a verification cache entry present:

   Rcpt To:<forw...@test.com>
   450 4.1.1 <forw...@test.com>: Recipient address rejected: unverified 
address: connect to gmail-smtp-in.l.google.com[142.250.138.26]:25: Connection 
timed out

      Logs show:

      Aug 27 11:31:15 dev postfix/smtpd[1091]: NOQUEUE: reject: RCPT from 
my.host.name[xx.xx.xx.xx]: 450 4.1.1 <forw...@test.com>: Recipient address 
rejected: unverified address: connect to 
gmail-smtp-in.l.google.com[142.250.138.26]:25: Connection timed out; 
from=<je...@my.host.name> to=<forw...@test.com> proto=ESMTP helo=<my.host.name>
      Aug 27 11:31:15 dev postfix/qmgr[11728]: 1224C210A0: 
from=<double-bounce3...@dev.server.tld>, size=275, nrcpt=1 (queue active)
      Aug 27 11:31:15 dev postfix/smtp[1235]: connect to 
gmail-smtp-in.l.google.com[2607:f8b0:4023:1006::1b]:25: Network is unreachable


        So the recipient address forw...@test.com triggered the verification,
      but the verification itself is being performed against the address I
      forwarded to, m...@gmail.com.  If I remove the mysql-verify_recipients.cf 
      check, the recipient is accepted:

   Rcpt To:<forw...@test.com>
   250 2.1.5 Ok

           I don't see any way to configure around this, but perhaps I'm
         overlooking something.  Or possible bug?

         Thanks,
         Jesse

         -- 
         Jesse Norell
Kentec Communications, Inc.
970-522-8107  -  www.kci.net