Extension icon in message lists

I had been using SpamSieve 3.0 under Sonoma. Today, I updated to version 3.0.1.

I noticed that new emails now have an extra icon in the message list. It looks like the same icon Apple uses for the Extensions preference in Mail. Here’s an example

(I haven’t gotten any spam since I upgraded so I don’t know if that icon will also appear on spam messages.)

Have you seen this? Does anyone know what’s causing it to appear?

The “puzzle piece” icon indicates that the message was touched by a Mail extension. This does not necessarily mean it was the SpamSieve extension, though. If you want to see whether the SpamSieve extension processed a message, you can look in SpamSieve’s Log window, and see what the Info ‣ Origin section says.

I only have the SpamSieve extension.

I hadn’t seen this icon before upgrading from SpamSieve 3.0 to 3.0.1 which is why I asked.

Perhaps that’s because there’s a macOS bug where in some cases Mail doesn’t send new messages to the extension. Sometimes reinstalling (or in this case updating) SpamSieve will tickle something in a macOS registry that seems to get it going again.

Well, I guess we’ll see if Apple addressed this bug as part of Sonoma 14.1 when it’s released next week. (I have the beta in a VM but only for testing my software, a Lisp Machine emulator.)

I am just noticing this myself, and am on Sonoma 14.2.1, along with a green message flag ( Add green flag to unread good messages)
I had not noticed this until the most recent SpamSieve update (3.0.3) but honestly I may have missed the puzzle piece.

They did not, but we added the Check inboxes for new messages not sent to Mail extension feature to work around the bug.

Sometimes installing an update temporarily gets Mail to use the extension again, thus adding the puzzle piece to the new messages.