I'm struggling to understand an aspect of SpamAssassin headers, and would greatly appreciate any help. Here is my scenario:
One of my mailbox addresses - say addr1@somewhere.com - is a member of a Mailman 3 mailing list.
I send a spam email (e.g. one with the GTUBE string) to the list from a different address. My mail server (Postfix/Amavis/Spamassassin) correctly identifies the mail as spam, and, appropriately, adds several spam-related headers - X-Spam-Flag, X-Spam-Score etc. I can see, from the copy of the email that lands in /var/lib/amavis/virusmails on the mail server, that those headers are indeed present.
The mail message is handed off to Mailman for processing. The list in question has nonmember_default_action set to "defer", so Mailman sends the message on to each member address.
However, the message, as it appears in the inbox of addr1@somewhere.com, contains no X-Spam- headers. The only indication of the message's spammish nature is in the Subject line, which has been prepended with the familiar string "***SPAM*****".
On the face of it, it looks like Mailman has removed the X-Spam-* headers. If that's so, I don't understand why. I would be very grateful if anyone could help me figure out what is going on here.
Thanks in advance, Stephen