Hello everyone
I have a setup where my smtp server is reachable through haproxy by
means of networking. But the outgoing email uses an exchange server (a
relay server to the outside world). So the relay server is only used for
sending emails. I do this out of necessity, since the smtp server is
internal, on a non-static ip address.
Everything is working well and correctly. The only problem I noticed is
that when an email bounces on the relay, it doesn't send the bounced
email back to the sender (from the relay to the smtpd server). I'm not
sure why this is the case, but I have a guess. This error in the logs:
```
postfix/smtp[301]: 6EA2E9F836DA: to=<u...@example.com>,
relay=mail.example.com[1.2.3.4]:25, delay=1.3, delays=0/0/1.3/0,
dsn=5.4.6, status=bounced (mail for example.com loops back to myself)
```
Well, as to this message, I understand that example.com matches
myhostname, so postfix doesn't know where to deliver that email.
Understandable. So after digging into docs, I went ahead and defined
`transport_maps` in the settings, with a line `example.com
smtp:10.10.100.100` (where 10.10.100.100 is the address where the smtp
receiving server can be found), used postmap on it to create the db
file, and that seems fine. But then I tried bouncing again, and got the
error:
```
postfix/smtp[299]: C0A3C9F906D0: to=<u...@example.com>,
relay=10.10.100.100[10.10.100.100]:25, delay=957, delays=950/0.02/6.4/0,
dsn=5.4.6, status=bounced (mail for 10.10.100.100 loops back to myself)
```
But... 10.10.100.100 is not the relay server address! It's the address
of the smtp server that is supposed to receive the bounced email. Why
does it think that this is "back to myself", but writing another
server's address?
The complete logs of the incident (in the relay) are as follows:
```
postfix/postfix-script[271]: starting the Postfix mail system
postfix/master[272]: daemon started -- version 3.7.11, configuration
/etc/postfix
postfix/postscreen[282]: cache btree:/var/lib/postfix/postscreen_cache
full cleanup: retained=0 dropped=0 entries
postfix/postscreen[282]: CONNECT from [10.10.100.100]:37598 to
[10.10.100.1]:61025
postfix/postscreen[282]: WHITELISTED [10.10.100.100]:37598
postfix/postscreen[282]: using backwards-compatible default setting
respectful_logging=no for client [10.10.100.100]:37598
postfix/smtpd[284]: connect from unknown[10.10.100.100]
postfix/trivial-rewrite[287]: warning: database
/etc/postfix/transport.db is older than source file /etc/postfix/transport
postfix/smtpd[284]: B57629F906CB: client=unknown[10.10.100.100]
postfix/cleanup[288]: B57629F906CB:
message-id=<a5e690ab-5dbd-488b-bac0-3c347982f...@example.com>
postfix/smtpd[284]: disconnect from unknown[10.10.100.100] ehlo=1 mail=1
rcpt=1 data=1 quit=1 commands=5
postfix/qmgr[274]: B57629F906CB: from=<u...@example.com>, size=10021,
nrcpt=1 (queue active)
postfix/smtp[289]: B57629F906CB:
to=<bouncet...@testtesttesttestytesttesttesttest.com>, relay=none,
delay=0.19, delays=0.17/0.02/0.01/0, dsn=5.4.4, status=bounced (Host or
domain name not found. Name service error for
name=testtesttesttestytesttesttesttest.com type=AAAA: Host not found)
postfix/cleanup[288]: EB0619F906D2:
message-id=<20240715131917.eb0619f90...@example.com>
postfix/bounce[290]: B57629F906CB: sender non-delivery notification:
EB0619F906D2
postfix/qmgr[274]: EB0619F906D2: from=<>, size=12122, nrcpt=1 (queue active)
postfix/qmgr[274]: B57629F906CB: removed
postfix/smtp[289]: warning: host 10.10.100.100[10.10.100.100]:25 greeted
me with my own hostname example.com
postfix/smtp[289]: warning: host 10.10.100.100[10.10.100.100]:25 replied
to HELO/EHLO with my own hostname example.com
postfix/smtp[289]: EB0619F906D2: to=<u...@example.com>,
relay=10.10.100.100[10.10.100.100]:25, delay=0.47, delays=0/0/0.47/0,
dsn=5.4.6, status=bounced (mail for 10.10.100.100 loops back to myself)
postfix/qmgr[274]: EB0619F906D2: removed
```
I would really appreciate some insight into how to properly solve this
problem, so that bounced emails are correctly delivered back to the smtp
server I point to.
Best regards,
Sam
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