Hello.
I was able to replicate this error, however it's not a misconfiguration
in Postfix, but rather a policy change by Google. I didn't notice the
bounce message sooner, since it was routed to my SPAM folder on Gmail.
If I use a GMAIL From: address and attempt to email another GMAIL
account, it bounces back with this error. Only, when I use a third-party
to relay the message. I think what is happening is that Google has
implemented a new anti-spam policy, rejecting any emails that have GMAIL
email hosted domain that is failing SPF/DKIM. Only messages relayed via
Google are valid. If you are using a contact form, the From: address is
typically munged to be the user filling out the form.
---------- Forwarded message ----------
From: Matthew McGehrin <x...@gmail.com>
To: Matthew McGehrin <x...@gmail.com>
Cc:
Bcc:
Date: Tue, 28 Nov 2023 20:25:24 -0600
Subject: Testing to Gmail
Test
<x...@gmail.com>: host gmail-smtp-in.l.google.com[142.251.167.27]
said: 550-5.7.26 This mail has been blocked because the sender is
unauthenticated. 550-5.7.26 Gmail requires all senders to
authenticate with
either SPF or DKIM. 550-5.7.26 550-5.7.26
Thank you.
Matthew
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