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  • Mail Lists with external receipients

Two years ago I was asink the same question (https://community.grommunio.com/d/584-mail-list-with-external-recepients)
In the meantime, Grommunio has made great progress and a customer has asked me to carry out another evaluation of mailing lists with internal and external recipients.
The positive result is that groups can be addressed easily using their email address and the received emails are distributed to the registered members - both externally and internally.
Unfortunately, some providers seem to be blocking outgoing emails due to a lack of compliance with RFC 5532 5322 (crpb). The Google mail servers, for example, refuse to deliver with error 550-5.7.1

An example can be seen here - from yesterday, recipient addresses are anonymized:

2024-11-17T00:33:42.386021+01:00 mail01 postfix/smtp[1803080]: Trusted TLS connection established to gmail-smtp-in.l.google.com[108.177.15.26]:25: TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256
2024-11-17T00:33:42.468437+01:00 mail01 postfix/smtp[1803085]: Trusted TLS connection established to mx01.t-online.de[194.25.134.72]:25: TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (secp384r1) server-signature RSA-PSS (4096 bits) server-digest SHA256
2024-11-17T00:33:42.657553+01:00 mail01 postfix/smtp[1803085]: EB9336150E: to=<12345@t-online.de>, relay=mx01.t-online.de[194.25.134.72]:25, delay=0.69, delays=0.11/0.16/0.3/0.12, dsn=2.0.0, status=sent (250 2.0.0 Message accepted.)
2024-11-17T00:33:42.657867+01:00 mail01 postfix/smtp[1803085]: EB9336150E: to=<6789@t-online.de>, relay=mx01.t-online.de[194.25.134.72]:25, delay=0.69, delays=0.11/0.16/0.3/0.12, dsn=2.0.0, status=sent (250 2.0.0 Message accepted.)
2024-11-17T00:33:42.799251+01:00 mail01 postfix/smtp[1803080]: EB9336150E: to=<xyz@gmail.com>, relay=gmail-smtp-in.l.google.com[108.177.15.26]:25, delay=0.76, delays=0.11/0.01/0.37/0.28, dsn=5.7.1, status=bounced (host gmail-smtp-in.l.google.com[108.177.15.26] said: 550-5.7.1 This message is not RFC 5322 compliant. There are multiple Reply-To 550-5.7.1 headers. To reduce the amount of spam sent to Gmail, this message has 550-5.7.1 been blocked. For more information, go to 550-5.7.1 https://support.google.com/mail/?p=RfcMessageNonCompliant and review 550 5.7.1 RFC 5322 specifications. ffacd0b85a97d-3821ae3228asi3952477f8f.474 - gsmtp (in reply to end of DATA command))
2024-11-17T00:33:42.830604+01:00 mail01 postfix/qmgr[658]: EB9336150E: removed

Now, Google is not the be-all and end-all, but it would be nice to be able to send emails from mailing lists to Gmail.
Does anyone have any ideas about this?

Fixed the rfc number (which was NFS 😛) and codeblock.

how many recipients are you talking?
the internal list should only be like one, e.g grp_food@moo.tld so only the outside recipients could be many or not?
But yeah, currently there is no header-information about groups but i don't think this would be too hard to do.

But google might also just bicker because the reputation of the sending server isn't that good?

Thanks for fixing the RFC - typo!
To avoid misunderstandings between internal and external, here is the clarification:
The list address only has one address:
list-adress@grommunio.domain

The members of the list can be internal and external addresses:
user1@grommunio.domain
user1@gmail.com
user1@t-online.de
user1@outlook.com

In the example, I had a total of 4 list members. One within the grommunio domain, 3 with external/foreign email addresses (contacts).
The grommunio users mail was deliverd to his grommunio mailbox as expected. Of the external ones, 2 were delivered without errors, the third (gmail) came back with the error message mentioned.
The sending mail server (not the grommunio server) has been processing the sending domain for years and is also "responsible" for around 20 other domains and can also talk to gmail. So I don't think there is a fundamental misconfiguration.
The error message also clearly refers to: "There are multiple Reply-To 550-5.7.1 headers, which IMHO indicates a problem with the composition of the mail.
Can't I teach Postfix - either the one from Grommunio or my frontend Postfix - to separate such emails and only send them to one recipient per send out?

  • crpb replied to this.

    A small addition: Has anyone ever experimented with smtpd_recipient_limit? If I set this limit to one...
    That would be a pretty dirty workaround, but maybe it will work.

    • crpb replied to this.

      Bob17 smtpd_recipient_limit

      uah, you could try but uff.. better open an issue at github with this if you can.

      Bob17 The sending mail server (not the grommunio server) has been processing the sending domain for years and is also "responsible" for around 20 other domains and can also talk to gmail.

      yeah, i already thought so but still had to say it :>.

      Here comes the next addition:
      Trying to solve the problem using "smtpd_recipient_limit" is a really stupid idea...
      Because only the first recipient on the list will be processed and the others will be discarded. So definitely not a solution!

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