You can either mail yourself a copy by including a ‘BCC’ header in the mail message, or store a copy of the message directly to a file by including an ‘FCC’ header.
If you use standard mail, you can automatically create a ‘BCC’ to yourself by putting
(setq mail-self-blind t)
in your init file (see How do I set up an init file properly?). You can automatically include an ‘FCC’ field by putting something like the following in your init file:
(setq mail-archive-file-name (expand-file-name "~/outgoing"))
The output file will be in Unix mail format.
If you use mh-e, add an ‘FCC’ or ‘BCC’ field to your
components file.
It does not work to put ‘set record filename’ in the .mailrc file.