A CRM’s email kept landing in spam. The server was not the cause.

Context

A UK client’s CRM sent notifications, invoices and confirmations. Some recipients got them, others did not.

Problem

The pattern was obvious once written down: messages vanished at Microsoft and Apple but arrived elsewhere. The explanation repeated until then was "IP reputation", which would have meant weeks of warming up a new IP for nothing.

What I did

1. 01Compared headers from recipients who received the mail and those who did not
2. 02Checked the policies published in DNS and how each provider actually evaluated them
3. 03Found the real cause: messages left the sending provider unsigned, which triggered quarantine at providers that enforce the policy strictly
4. 04Documented exactly what had to change, and who had to change it