Verify receivers - SMTP Recipient rejection inconsistency

[AirForLife]

Hello,
I'm getting inconsistent results with Verify Receivers - Yes (550) results.

Some emails get rejected at SMTP level as it should be, after double-bounce verification.

Spoiler

Nov 25 14:00:03 AV1 postfix/smtpd[2594]: connect from smtp31.easymailpost.eu[217.146.76.94]
Nov 25 14:00:09 AV1 postfix/smtpd[2594]: NOQUEUE: reject: RCPT from smtp31.easymailpost.eu[217.146.76.94]: 550 5.1.1 <internal.recipient@internal.domain>: Recipient address rejected: undeliverable address: host internal.mailserver [xx.xx.xx.xx] said: 550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup (in reply to RCPT TO command); from=<external.user@external.domain> to=<internal.recipient@internal.domain> proto=ESMTP helo=<smtp31.easymailpost.eu>
Nov 25 14:00:09 AV1 postfix/smtpd[2594]: disconnect from smtp31.easymailpost.eu[217.146.76.94] ehlo=2 starttls=1 mail=1 rcpt=0/1 data=0/1 rset=1 quit=1 commands=6/8

Some emails are accepted and then bounced resulting in NDR from Mailer-daemon.

Spoiler

Nov 25 14:06:07 AV1 postfix/smtpd[7738]: connect from mail-eopbgr80078.outbound.protection.outlook.com[40.107.8.78]
Nov 25 14:06:07 AV1 postfix/smtpd[7738]: 6CC7C230A6: client=mail-eopbgr80078.outbound.protection.outlook.com[40.107.8.78]
Nov 25 14:06:07 AV1 postfix/cleanup[7714]: 6CC7C230A6: message-id=<AM0PR040215836F2FBF10F755235A838B4A0@AM0PR040215.eurprd04.prod.outlook.com>
Nov 25 14:06:07 AV1 postfix/qmgr[32156]: 6CC7C230A6: from=<external.user@external.domain>, size=45672, nrcpt=1 (queue active)
Nov 25 14:06:07 AV1 postfix/smtpd[7738]: disconnect from mail-eopbgr80078.outbound.protection.outlook.com[40.107.8.78] ehlo=2 starttls=1 mail=1 rcpt=1 bdat=1 quit=1 commands=7
Nov 25 14:06:07 AV1 pmg-smtp-filter[9004]: 2338E5DDBC3AF9B87F: new mail message-id=<AM0PR040215836F2FBF10F755235A838B4A0@AM0PR040215.eurprd04.prod.outlook.com>#012
Nov 25 14:06:09 AV1 pmg-smtp-filter[9004]: 2338E5DDBC3AF9B87F: SA score=0/5 time=1.922 bayes=0.00 autolearn=no autolearn_force=no hits=BAYES_00(-0.1),DKIM_SIGNED(0.1),DKIM_VALID(-0.1),HTML_FONT_LOW_CONTRAST(0.001),HTML_MESSAGE(0.001),KAM_SHORT(0.001),MISSING_HEADERS(1.021),RCVD_IN_DNSWL_NONE(-0.0001),SPF_HELO_PASS(-0.001),SPF_PASS(-0.001)
Nov 25 14:06:09 AV1 postfix/smtpd[8396]: connect from localhost.localdomain[127.0.0.1]
Nov 25 14:06:09 AV1 postfix/smtpd[8396]: B4CB0233A4: client=localhost.localdomain[127.0.0.1], orig_client=mail-eopbgr80078.outbound.protection.outlook.com[40.107.8.78]
Nov 25 14:06:09 AV1 postfix/cleanup[7707]: B4CB0233A4: message-id=<AM0PR040215836F2FBF10F755235A838B4A0@AM0PR040215.eurprd04.prod.outlook.com>
Nov 25 14:06:09 AV1 postfix/qmgr[32156]: B4CB0233A4: from=<external.user@external.domain>, size=46616, nrcpt=1 (queue active)
Nov 25 14:06:09 AV1 postfix/smtpd[8396]: disconnect from localhost.localdomain[127.0.0.1] ehlo=1 xforward=1 mail=1 rcpt=1 data=1 commands=5
Nov 25 14:06:09 AV1 pmg-smtp-filter[9004]: 2338E5DDBC3AF9B87F: accept mail to <internal.recipient@internal.domain> (B4CB0233A4) (rule: default-accept)
Nov 25 14:06:09 AV1 pmg-smtp-filter[9004]: 2338E5DDBC3AF9B87F: processing time: 2.156 seconds (1.922, 0.081, 0)
Nov 25 14:06:09 AV1 postfix/lmtp[6428]: 6CC7C230A6: to=<internal.recipient@internal.domain>, relay=127.0.0.1[127.0.0.1]:10024, delay=2.4, delays=0.15/0/0.05/2.2, dsn=2.5.0, status=sent (250 2.5.0 OK (2338E5DDBC3AF9B87F))
Nov 25 14:06:09 AV1 postfix/qmgr[32156]: 6CC7C230A6: removed
Nov 25 14:06:14 AV1 postfix/smtp[8663]: B4CB0233A4: to=<internal.recipient@internal.domain>, relay=internal.mailserver [xx.xx.xx.xx]:2525, delay=5.1, delays=0.05/0/0.05/5, dsn=5.1.10, status=bounced (internal.mailserver [xx.xx.xx.xx] said: 550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup (in reply to RCPT TO command))
Nov 25 14:06:24 AV1 postfix/qmgr[32156]: B4CB0233A4: removed

Any ideas why some emails are accepted instead of being rejected at SMTP session?

 

[Stoiko Ivanov]

hmm - maybe in the second case the address internal.recipient@internal.domain did exist before and that positive result was cached?
you can discard the current verification database in the GUI -> Administration -> Queues


I hope this helps!

 

[AirForLife]

Unfortunately, discarding verification DB doesn't help.
If i send mail to random1234567890username@internal.domain, it gets same queued/bounced result 1st-2nd-3rd time too.


Another finding, if i send mail to recipient, that got double-bounce check and is rejected correctly at SMTP level from another sender, it still generates bounce from Proxmox server for my test mail.

 

[Stoiko Ivanov]

hmm - in the case where recipient verification works it seems the downstream server is reached via port 25 (no :2525 in the logline)
in the case where it does not work the downstream server is reached on port 2525

if it's 2 different servers I'd compare the settings of those