The
X-Spam-known-sender header shows whether address book whitelisting was triggered:
- no
- The From address was not found in the address book.
- yes ("Address whatever@example.org in From header is in addressbook");
- The From address was found in the address book. After the phrase shown above you will see a list of address book folders which contain that address. For each listed folder you will see a pseudorandom hex tag which refers to that folder.
- Messages from Fastmail staff (which show the green checkmark) have a different phrase after the yes marking.
As far as I can tell, it makes no difference which category (personal, work, or other) you use or how many addresses you add to one contact entry. In all cases I have checked the address is properly detected and causes whitelisting.
There are certain circumstances (such as DMARC failure) in which it appears that the From address is spoofed. In these cases Fastmail will not whitelist the message and you will see a
X-Spam-known-sender header such as:
X-Spam-known-sender: no ("Email failed DMARC policy for domain")
Bill