extract smtpmail data from .authinfo (or .authinfo.gpg)?

[Tom Roche <Tom_Roche@pobox.com>]

summary: To send email, I currently use smtpmail and .authinfo: the
latter doesn't store any passwords, but does have hostname, id, and
port. The latter are duplicated in an elisp file I load from my init.el.
I'd prefer to have the latter use, or read the data from, .authinfo:
how to do?

details:

I'm using

GNU Emacs 23.3.1 (x86_64-pc-linux-gnu, GTK+ Version 2.24.4)
 of 2011-04-10 on brahms, modified by Debian

on

$ lsb_release -ds
Linux Mint Debian Edition
$ uname -rv
2.6.39-2-amd64 #1 SMP Tue Jul 5 02:51:22 UTC 2011

I send email using plain smtpmail configured by a file name=tlrMail.el
which I load from init.el. Among other things (like

(require 'smtpmail)

) tlrMail loads some SMTP info, e.g.,

(setq foo-smtp-server-port 26)
(setq foo-smtp-server-hostname "smtp.foo.com")
(setq foo-user-mail-id "me")
(setq foo-starttls-credentials
  (list (list foo-smtp-server-hostname foo-smtp-server-port 'nil 'nil)))

where "foo" is like a profile name in some email clients. This works,
but it duplicates data that's also in my .authinfo (e.g.,

machine smtp.foo.com login me port 26

). Is there a way I can make my elisp use .authinfo directly, or scrape
the relevant data from .authinfo? Or better yet, from .authinfo.gpg?
(And I'd appreciate pointers to tutorials regarding use of
.authinfo.gpg, and GPG with smtpmail generally.)

Feel free to reply directly to me as well as the list.
Your suggestions are appreciated, Tom Roche <Tom_Roche@pobox.com>