Under normal circumstances, Apple Mail does not crash, whether or not you are using SpamSieve. If you find that Mail is crashing, here are some things that you can do:
First, please send us a crash report so that we can look into the cause. Note that if you are seeing a spinning beachball cursor rather than a crash report window, Mail is probably hanging rather than crashing. In that case, you should instead see the If Apple Mail Is Running Slowly section of the manual.
Often, it helps just to restart your Mac.
Make sure that any other Mail plug-ins are updated to their latest versions. If that doesn’t help, see whether disabling the other plug-ins stops the crashes.
The most common Mail crash that we see is due to a bug in Mail’s own junk mail filter. SpamSieve normally tells Mail which messages it thinks are junk in order to protect you from Web bugs. Resetting Mail’s junk database may fix the problem.
You can also tell SpamSieve not to mark the messages as junk if analyzing the spam messages is causing Mail’s filter to crash. To do this, click the link for AppleMailPlugInSetIsJunk in the Esoteric Preferences.
Try renaming the SpamSieve rule in Mail to Move to Spam. This will cause Mail to treat it like a regular rule, bypassing SpamSieve. If Mail still crashes when applying the rule, this will show that the crash is due to Mail moving the message to the spam mailbox and not because of SpamSieve.
This test will cause Mail to move all incoming messages to the spam mailbox. After the test, you can disable the rule, move the messages back to the inbox, and use the Message ‣ Apply Rules command to re-filter them.
SpamSieve works with a variety of mail programs. You could temporarily use a different one, either for reading your mail or just for spam filtering. With an IMAP or Exchange mail account, you will see the same mailboxes and messages in each mail program.