A small number of users have reported that, when SpamSieve’s background filtering asks Mail to move a message to the Junk mailbox, Mail shows an error alert that says something like:
The message “<subject>“ could not be moved to the mailbox “<account name>“
The specified object was not found in the store., The process failed to get the correct properties.
This seems to mostly, if not exclusively, happen with Exchange accounts. There are several separate problems that can manifest in this same way, including damage to Mail’s files and possibly bugs in Mail itself or the mail server. If you record sample log when the alert appears and contact us, we can investigate and try to determine specifically what is happening on your Mac. However, here are some potential solutions that you can try yourself and that will likely resolve the problem: