Hi Bruce,
I'm on 8.58 and still having trouble with this issue (attachments not being sent out).
I've got an email going out that has both embedded images and possibly attachments (depending on what the user selects).
If the email gets sent without any attachments, all works fine.
If they tick one of the attachment (different pdfs) options, the email gets sent without the attachment AND with the embedded images set as attachments (screenshot attached).
I'm not sure how to replicate this is an example, as it's obviously fixed for most folk in 8.54.
I've done a full recompile.
Will try sending without any images embedded, see if that's something or just a red herring.
Stu