Attach mails as attachments in Mutt

We all know how to attach a file as an attachment in Mutt. Just press a in attach mode, and either type the file name or press ? to open up a file list.

But what to do when it comes to attaching a mail or even mails? For a single mail, just forward it. For multiple mails, here's what I found. Mutt has a command attach-message, which is default bind to A. The help message says,

A      attach-message                  attach message(s) to this message

It is a little bit confusing after pressing A and choose a mail box to open up. You just need to press t to tag any messages you want to attach and press q to return to the attach mode. Then you will see those messages appear in the attachment list.

Moreover, you can press ^D on a message to toggle it between inline and attachment.

^D     toggle-disposition              toggle disposition between inline/attachment