I don't know if this is the proper place for this, but I couldn't find this issue anywhere else. I tried to search Gemini for this issue, but the search didn't help me find anything on the Bulk email module.

I've discovered that adding attachments to messages when the file to be attached is in a secure
folder causes problems.

In Asynch. mode:
The Bulk Mail module doesn't indicate an error, but the only email I ever get is an "SMTP configuration test" email. If I add an attachment that is not in a secure folder, it seems to work.

In Sync mode:
I get the message:  No Messages were sent, you may want to check the Event Viewer to see if any Exceptions were logged.
There is no Exception logged in the event viewer.