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?