Can't forward attachments

The problem you are seeing is a side-effect of the limited HTML capabilities of MailMate. The composer in MailMate is essentially plain text only. This makes it a challenge to forward (and some times reply) to certain “complex” emails. Currently, MailMate falls back to attaching the email when forwarding when it cannot inline it (this is when you see a seemingly empty message). This is equivalent to “Message > Forward as Attachment”.

(In some cases, it might help to select text before forwarding since this changes how MailMate creates the forwarded message. In other cases, using “Message ▸ Redirect” might be more appropriate than forwarding.)

That said, I'm aware that this is a problem for many users and I'm actively working on a better way to handle it. Essentially it's going to mean that MailMate can forward/reply as well as any email client with an HTML composer while still only having a plain text composer itself (which is unlikely to change). I cannot give you a time frame, but it's a high priority item under active development (it's a complex issue even for HTML capable email clients since HTML is really a broken concept with respect to use in emails).

There are other tickets tracking progress on the HTML capabilities of MailMate, so I'm closing this ticket. You can still comment if you have additional questions.