mail-source-fetcher-alist

mail-source-fetcher-alist is a variable defined in `mail-source.el'.
Its value is

((file mail-source-fetch-file)
 (directory mail-source-fetch-directory)
 (pop mail-source-fetch-pop)
 (maildir mail-source-fetch-maildir)
 (imap mail-source-fetch-imap))

Documentation:
A mapping from source type to fetcher function.