I maintain several web sites containing at least one web form. Forms are
sent to my established postfix server to be turned into properly
constructed email and sent on. The server is used for many conventional
emails per day and set up to provide suitable dkim etc. All domains have
correct SPF, DKIM and DMARC records. No problem with receiving these
forms at relevant clients' and my own mailboxes.
The forms also send a copy to the sender as confirmation. Most of these,
as far as I know, get delivered but recently gmail has been rejecting
them with the message:
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 Authentication results:
550-5.7.26 DKIM = did not pass
550-5.7.26 SPF = did not pass
I have sent a form confirmation to my protonmail account and it passes
with no problem; spf, dkim and dmarc are all valid/pass.
Anyone know why this could be so, please?
If someone wishes to check this, a typical form (which is sent to me
with copy to "you") is at
https://www.linkcheck.co.uk/
under menu option Contact & Enquiries.
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