We only support NNTP as inputs for convert, import, and
mark|tag. I'm not sure if supporting NNTP output is worth
it, nor do we have a good way to test it.
Destination for results (e.g., C<path/to/Maildir>,
C<imaps://user@mail.example.com/INBOX.test>, or
C<mboxcl2:path/to/mbox>). The prefix may be a supported protocol:
-C<imap://>, C<imaps://>, C<nntp://>, or C<nntps://>. URLs requiring
+C<imap://> or C<imaps://>. URLs requiring
authentication must use L<netrc(5)> and/or L<git-credential(1)> to
fill in the username and password.