Invalid base64 string for MIME content

Help. I’m getting a constant stream of these pop-up messages on SpamSieve 3.0.1: The message “xxxxxx” could not be moved to the mailbox “xxxxxx”

Could you post a screenshot of this error? Does it happen in response to something that you are doing in Mail?

Where are you seeing the “Invalid base64 string for MIME content”?

I assume it was coming from SpamSieve running against new emails.
I got about 1-2 dozen, then they stopped.

Screenshot 2023-10-26 at 4.13.33 PM

I don’t think this would be related to SpamSieve, and it doesn’t look like it was referring to the Junk mailbox.

Sorry for the delay. Thank you for the super quick response.
It’s most likely just a coincidence. Thanks again!