Adding to what has been reported before by somebody else, but in some more detail, hope you can help:
MailMate claims to be handing over the message to SpamSieve:
1 new messages detected (SpamSieve detection is enabled) Part of query: $'B484BD0B-0941-4DED-9A39-C8C59B91272C'.filter(#flags.flag !=[x] '$NotJunk').filter(#import-date !exists) (8366 messages) SpamSieve -> MailMate: Message 704311 is good (0) – From: “C-Command Software Forum <email@example.com>”, Subject: “[C-Command] Confirm your new account”, Message-ID: firstname.lastname@example.org
SpamSieve claims to be receiving an empty message:
2021-03-21 14:29:53.278 [com.c-command.SpamSieve] Empty message
which then causes it to handle all incoming mail identically, because they all look identical:
Predicted: Gut (0) Subject: <SpamSieve-Unknown-Subject> From: <SpamSieve-Unknown-From> Identifier: mGchMm62dFNB53dkuohH0Q== Reason: looked up message in corpus Date: 2021-03-21 14:29:53 +0100 (GMT+1)
Running MailMate 1.14 (5757, x86) and SpamSieve 2.9.43 on macOS 11.2.3 (20D91).
The Automation permission has been requested and approved.
What is the next step for debugging?
(Please excuse the countless code blocks, but without them all sorts of links were generated automatically, which meant I was unable to create the topic because new users are only allowed to include two links.)