When that automatic move wasn’t working after the upgrade from macOS Catalina, and still using SpamSieve v2.9.45, I confirmed that: (1) The 3 SpamSieve entries are in the Mail (Version 14.0 (3654.120.0.1.13)) Message menu are present; (2) Mail->Prefences->Manage Plug-ins has SpamSieve.mailbundle checked; (3) Mail->Rules has “SpamSieve” as the first Rule and it’s checked; (4) System Preferences->Full Disk Access has SpamSieve.app checked; but System Preferences>Security & Privacy->Privacy->Files and Folders has SpamSieve.app grayed out (along with many more entries). Suggestions, please, for restoring the automatic moving of mail that has been trained as Spam to that Junk folder.
Addendum: While the subject cites that the “Junk” folder is in my On My Mac list, the Mail Rule [#3 above] has the action “Move Message to mailbox All Junk”.
Please follow the “Testing That the Rule Works” instructions on this page and, if it doesn’t work use the Save Diagnostic Report command in the Help menu and send me the report file, as described here.
Failed the “Testing That the Rule Works” steps ; sent the Diagnostic Report. 
Thanks for sending the report. I do see in the log that you trained the test message as spam and then applied the rules and SpamSieve thought it was spam. So Mail should have moved it to the Junk mailbox, as specified in your SpamSieve rule. You may be running into a Mail bug where it deletes messages instead of moving them. If so, it should help to configure Mail so that your Junk mailbox is on the server rather than under On My Mac.
Michael: Before I do that configuration (thanks), should it work with my Mail account as it is (deliberately) still a POP/POP3 rather than IMAP?
The Mail bug in question does not affect POP accounts as far as I know. So it’s not clear what’s happening here, and the suggested workaround is not possible because POP doesn’t support server mailboxes. I recommend enabling the backup feature. And it might help to create your own Spam mailbox and set the rule to use that instead of Junk, in case there’s something about your Junk mailbox that’s triggering the problem.
Update Michael: As a first step, I did NOT enable the backup feature, but did the creation of my own On My Mac Spam mailbox and changed the rule to it. Bottom Line: All of my all-ready Trained as Spam e-mails are now being moved directly to that new, On My Mac Spam mailbox; however, both my earlier “trials” of a freshly trained as Spam e-mail, at some point in time, went to the still-existing On-My-Mac Junk mailbox.
The only “extra” step I now have to do in the Spam mailbox successfully to use its Erase Spam command and the following request for confirmation is first to select all the e-mails in Spam—something I didn’t have to do when using the Junk mailbox.
So, for now, I’m leaving the Rule ciing the Spam mailbox and will report if I find a newly Trained as Spam still, at some point (still with the revised Rule), ends up in Junk.
Oops, below is a replacement for this 2nd paragraph in my last reply: The only “extra” step I now have to do in the Spam mailbox successfully to use its Erase Spam command and the following request for confirmation is first to select all the e-mails in Spam—something I didn’t have to do when using the Junk mailbox.
The replacement is:
The only “extra” steps I now have to do in the Spam mailbox successfully to use its Erase Junk Mail…—Note: NOT an Erase Spam Mail…— and the following request for confirmation is first to leave the entries as Unread and then to Select all the those unread e-mails in the Spam mailbox—somethings I didn’t have to do when using the Junk mailbox and its Erase Junk Mail…
Double Oops. I waited too long to edit my replacement of the original 2nd paragraph. My apologies to all. It should be:
The steps I now have to do in the Spam mailbox to delete its contents does not involve it’s command as it is Erase Junk Mail…—Note: NOT an Erase Spam Mail—and if used, it brings up the confirmation about erasing the contents of the Junk mailbox. Instead, I left the entries as Unread, then Selected all the those unread e-mails in the Spam mailbox, and then do a Command–Delete. (I didn’t check whether a plan Delete would also have worked.)
It sounds like you are saying that the Mail rule is able to move messages to Spam but not to Junk. If you want to keep using it with Spam, that’s fine. However, normally both should work, and it may be worth rebuilding Mail’s database to try to get moving to Junk to work.
- Yes; I’ll continue with the Rule citing Spam. (I’ll also be seeing whether an initial Train as Spam causes that e-mail to go to the Junk folder.)
- Any thoughts as to why these options that appear for the Spam folder include an Erase option that cites Junk (as does the confirmation that follows selecting it)?
- Although I’ve held off doing the complete rebuid, I did the quick rebuild of the All inboxes just in case.
I believe Mail shows the same contextual menu for all mailboxes. Some of the commands apply to the particular selected mailbox; others don’t and are just shortcuts for commands in the menu bar.
Thanks.