Hi everyone,
I’m using Mailcow to manage several email domains. One of these domains is configured in a hybrid setup with Microsoft 365 (some mailboxes are hosted on Microsoft 365, others on Mailcow).
On this particular domain, I’m regularly experiencing mail rejections with the following entries in the Mailcow / Rspamd logs:
FREEMAIL_POLICY_FAILURE • FREEMAIL_FROM & !DMARC_POLICY_ALLOW & !MAILLIST & !WHITELISTED_FWD_HOST & -g+:policies (16)
R_DKIM_REJECT (8) [gmail.com:s=20230601]
IP_REPUTATION_HAM (-1.220178) [asn: 8075(-0.39), country: US(-0.01), ip: 40.93.76.27(-0.82)]
ARC_ALLOW (-1) [microsoft.com:s=arcselector10001:i=1]
MV_CASE (0.5)
DMARC_POLICY_SOFTFAIL (0.1) [gmail.com : No valid SPF,none]
MIME_GOOD (-0.1) [multipart/alternative,text/plain,multipart/related]
R_SPF_SOFTFAIL (0.1) [all:c]
MX_GOOD (-0.01) []
BAYES_HAM (-0.006771) [43.28%]
The exact same message sent to another domain configured the same way (but not hybrid) doesn’t cause any issues.
Has anyone encountered this before or have any ideas on why this rejection is happening, and why it only affects this hybrid Mailcow / Microsoft 365 domain?
It only seems to happen when emails are forwarded from freemail senders (like Gmail, Outlook, Orange.fr, Laposte.fr, etc.).
Thanks in advance for your help!