OVERWRITE_FROM does not work

[Toutzn]

  postfix:
    image: juanluisbaptiste/postfix:latest
    restart: always
    environment:
      - SMTP_SERVER=myhost.domain.ltd
      - SMTP_PORT=587
      - SMTP_USERNAME=sm-localdocker@user
      - SMTP_PASSWORD=123123123123
      - SERVER_HOSTNAME=localhost
      - OVERWRITE_FROM=monitoring@mydomain.ltd
    volumes:
      - "/etc/localtime:/etc/localtime:ro"

Describe the issue
As I try to rewrite the from address via OVERWRITE_FROM, it doesn't work:

Dec 16 12:09:02 pfx-nag postfix/master[1]: daemon started -- version 3.10.4, configuration /etc/postfix
Dec 16 12:09:29 pfx-nag postfix/smtpd[99]: connect from nagios-nagios-1.nagios_default[192.168.16.2]
Dec 16 12:09:29 pfx-nag postfix/smtpd[99]: 09EF34F7: client=nagios-nagios-1.nagios_default[192.168.16.2]
Dec 16 12:09:29 pfx-nag postfix/cleanup[102]: 09EF34F7: message-id=<20251216110928.E7A967010@af5be243f321>
Dec 16 12:09:29 pfx-nag postfix/smtpd[99]: disconnect from nagios-nagios-1.nagios_default[192.168.16.2] ehlo=1 mail=1 rcpt=1 data=1 quit=1 commands=5
Dec 16 12:09:29 pfx-nag postfix/qmgr[97]: 09EF34F7: from=<root@af5be243f321>, size=591, nrcpt=1 (queue active)
Dec 16 12:09:29 pfx-nag postfix/smtp[103]: 09EF34F7: to=<XXXXXXXXXXXXXXX>, relay=mailrelay.mydomain.ltd[XXXXXXXXXXXXX]:587, delay=0.44, delays=0.02/0.04/0.31/0.08, dsn=5.5.2, status=bounced (host mailrelay.mydomain.ltd[XXXXXXXXXXXXX] said: 504 5.5.2 <root@af5be243f321>: Sender address rejected: need fully-qualified address (in reply to RCPT TO command))
Dec 16 12:09:29 pfx-nag postfix/cleanup[102]: 799144FC: message-id=<20251216110929.799144FC@pfx-XXXXXXXXX>
Dec 16 12:09:29 pfx-nag postfix/bounce[105]: 09EF34F7: sender non-delivery notification: 799144FC
Dec 16 12:09:29 pfx-nag postfix/qmgr[97]: 799144FC: from=<>, size=2693, nrcpt=1 (queue active)
Dec 16 12:09:29 pfx-nag postfix/qmgr[97]: 09EF34F7: removed
Dec 16 12:09:29 pfx-nag postfix/smtp[103]: connect to mailrelay.mydomain.ltd[2a01:4f8:1c1c:365e::1]:587: Address not available
Dec 16 12:09:29 pfx-nag postfix/smtp[103]: 799144FC: to=<root@af5be243f321>, relay=mailrelay.mydomain.ltd[XXXXXXXXXXXXX]:587, delay=0.29, delays=0.01/0/0.25/0.04, dsn=5.5.2, status=bounced (host mailrelay.mydomain.ltd[XXXXXXXXXXXXX] said: 504 5.5.2 <root@af5be243f321>: Recipient address rejected: need fully-qualified address (in reply to RCPT TO command))
Dec 16 12:09:29 pfx-nag postfix/qmgr[97]: 799144FC: removed

As you can see the from will not override as it needed to send the mail from.

from=<root@af5be243f321>

Also I I use mail -s "test" -a "from:myeimal.domain.ltd" it does not work because the from will no update to the right value

[juanluisbaptiste]

@Toutzn the OVERWRITE_FROM is working as expected for me:

mail -s "Testing OVERWRITE_FROM" juan@xxxxx.tech

And on the logs:

postfix-1  | Dec 25 20:40:36 correo postfix/pickup[96]: B8F4D11E02C7: uid=0 from=<root>
postfix-1  | Dec 25 20:40:36 correo postfix/cleanup[113]: B8F4D11E02C7: message-id=<20251226014036.B8F4D11E02C7@correo.xxxxx.tech>
postfix-1  | Dec 25 20:40:36 correo postfix/qmgr[97]: B8F4D11E02C7: from=<root@xxxxx.tech>, size=451, nrcpt=1 (queue active)
postfix-1  | Dec 25 20:40:39 correo postfix/smtp[116]: B8F4D11E02C7: replace: header From: root <root@xxxxx.tech>: From: test@xxxxx.tech
postfix-1  | Dec 25 20:40:39 correo postfix/smtp[116]: B8F4D11E02C7: to=<juan@xxxxx.tech>, relay=smtp.maileroo.com[167.235.217.250]:587, delay=3.1, delays=0.02/0.02/2.3/0.81, dsn=2.0.0, status=sent (250 Accepted)
postfix-1  | Dec 25 20:40:39 correo postfix/qmgr[97]: B8F4D11E02C7: removed

Maybe the issue is the way you are testing? you don't need to add the from header on the client, that's what the OVERWRITE_FROM config option does for you at the server level.

[Toutzn]

Interesting, as you can see in my case it won't work. only if I add the changes as you can see in my MR. It also makes no difference whether I try to overwrite something with mail -a “FROM:” or not. I am well aware that I don't need to do this. That's what the variable is for.
My change just ensures that this definitely happens and that the correct sender address is provided when logging into Postfix via authentication. In my case, this is important because the relay server looks specifically at this field and only lets the emails through if it matches.

[juanluisbaptiste]

After reading the documentation of the canonical table, I see that what we currently do only changes the sender at the header level, but doesn't change the SMTP envelope sender (Return-Path, bounce address), and may cause SPF/DKIM issues.

Please address the comments in the PR so we can merge it, thanks!