The API is still shaky.

@section Init/Destroy

Initialize the mailer object.

@deftypefun int mailer_init (mailer_t *@var{mailer}, const char *@var{name}, int @var{flag})
Not Implemented.

@defmac MU_ML_PROGRAM
Program like Sendmail, mail, mailx to deliver the mail
@end defmac

@defmac MU_ML_SMTP
Contact the host directly with SMTP.
@end defmac

@defmac MU_ML_MPP
Use MPP protocol.
@end defmac

@end deftypefun

@deftypefun int mailer_destroy (mailer_r *@var{mailer})
Not Implemented.
@end deftypefun

@section Open/Close

@deftypefun int mailer_open (mailer_t @var{mailer}, int @var{flag})
On mailer program, it is a @code{stat(2)} or ping a server for SMTP.
@end deftypefun
@deftypefun int mailer_close (mailer_t @var{mailer})
Noop on most mailers.
@end deftypefun

@section Sending

Sending a message.

@deftypefun int mailer_new_message (mailer_t @var{mailer}, size_t *)
Not Implemented.
@end deftypefun

@deftypefun int mailer_send (mailer_t @var{mailer}, message_t @var{msg}, int destroy)
@var{msg} is delivered
@end deftypefun

@section Notification
@deftypefun int mailer_set_delivery_cb (mailer_t @var{mailer}, message_t @var{msg}, int *@var{notification}(mailer_t @var{mailer}, int @var{status}, size_t @var{msgno}, void *@var{arg})
On delivery @code{notification (mailer, status, msgno, arg)} is
executed.
@end deftypefun

@section SMTP
@cindex SMTP

TODO: describe protocol, URL, mailto URL etc ..

@section UUCP
@cindex UUCP

 ! It this to old ? Is it worth it ?

@section Program
@cindex Sendmail
@cindex mailx
@cindex mail

This is not a protocol, but on must site the delivery of mail is done via
a program, @command{/usr/lib/sendmail}, @command{/bin/mailx},
@command{/bin/mail}, @dots{}

@section MPP
@cindex MPP

Mail Posting Protocol.  Not Implemented.