Caesar rotate (aka. rot13) the current message (message-caesar-buffer-body). If narrowing is in effect, just rotate the visible portion of the buffer. A numerical prefix says how many places to rotate the text. The default is 13.

Elide the text between point and mark (message-elide-region). The text is killed and an ellipsis (`[...]') will be inserted in its place.

Kill all the text up to the signature, or if that's missing, up to the end of the message (message-kill-to-signature).

Delete all text in the body of the message that is outside the region (message-delete-not-region).

Insert four newlines, and then reformat if inside quoted text.

Here's an example:

> This is some quoted text.  And here's more quoted text.

If point is before `And' and you press M-RET, you'll get:

> This is some quoted text.

*

> And here's more quoted text.

`*' says where point will be placed.

Insert a To header that contains the Reply-To or From header of the message you're following up (message-insert-to).

Insert a Newsgroups header that reflects the Followup-To or Newsgroups header of the article you're replying to (message-insert-newsgroups).

Rename the buffer (message-rename-buffer). If given a prefix, prompt for a new buffer name.