How to pipe text or load a file directly into mail-mode?

[Adam Funk]

I'd like the output of a Perl program to end up in an Emacs mail-mode
buffer, ready to proofread, edit and then send with C-c C-c.  I don't
mind whether my program

1. pipes the output to an emacs command, or

2. saves the output in a temp file and opens it with an emacs command.

Which is easier for the emacs command to handle (I expect 2)?

What command-line arguments to emacs do I need for this to work?

Does the program's output (emacs's input) need to be formatted in the
normal way for a mail message (with a blank line after the headers) or
the way it shows up in the Emacs mail buffer (with "--text follows
this line--" after the headers)?

Thanks,
Adam