We try to ensure that SpamSieve is compatible with other Apple Mail plug-ins. Nevertheless, it is possible for another plug-in—especially an old version—to prevent SpamSieve or Mail from working properly.
Known Issues
GPGMail
There is a known bug in the GPGMail plug-in that causes it to re-apply Mail’s rules (including SpamSieve) to non-new messages and even to sent messages.
MailTags
MailTags has generally been fully compatible with SpamSieve. Please make sure that you are using the latest version of MailTags. If you encounter any problems, see if disabling it helps.
Troubleshooting
If you are using multiple Mail plug-ins and seeing hangs, problems launching, or other unexpected behavior, it’s best to check whether the problem goes away when only the SpamSieve plug-in is installed.
On macOS 10.14 and later, you can disable Mail plug-ins by unchecking them from Settings ‣ General ‣ Manage Plug-ins….
On earlier versions of macOS, Mail plug-ins can be installed in the global Bundles folder (which not all users will have):
/Library/Mail/Bundles
and also in the user Bundles folder:
/Users/<username>/Library/Mail/Bundles
To access this folder, see the How can I open the Library folder? section.
Please check both Bundles folders for any .mailbundle files/folders. You can temporarily disable a plug-in by dragging its .mailbundle to your desktop and then re-launching Mail.
If disabling the other Mail plug-ins fixes the problem: