Apple just released version 10.6.5 of OS X, and it updated Mail.app and the corresponding Message.framework. This means that if you are a user of the SpamSieve plugin for spam filtering in Mail.app, it will disable the bundle upon launch and tell you that it needs to be updated. Fortunately, the fix for this is simple:

  1. Find SpamSieve.mailbundle in your ~/Library/Mail folder. It will be in a Bundles (Disabled) folder if you already launched Mail.app once, if not it will be in the Bundles folder.
  2. Inside the Contents folder of SpamSieve.mailbundle, open up the Info.plist file in Property List Editor*.
  3. Add the following two keys to the SupportedPluginCompatibilityUUIDs array:
    • 857A142A-AB81-4D99-BECC-D1B55A86D94E
    • BDD81F4D-6881-4A8D-94A7-E67410089EEB
  4. Save the file, and if necessary, move the .mailbundle file out of the Bundles (Disabled) folder and into the “Bundles” folder.
  5. Relaunch Mail.app.

* If you don’t have Property List Editor and would rather not download the whole Developer Tools package to get it (I don’t blame you!), then feel free to download my edited copy of the Info.plist file. Simply replace the Info.plist file in your SpamSieve.mailbundle with the one I just linked to.