can't send mail to hotmail or yahoogroups addresses

[Eliot Stock]

Hello.

With FC2 I thought I'd have a go at hosting my own mail for the first
time. Sendmail, procmail, and Dovecot are all working fine, but
hotmail and yahoogroups seem to be refusing to accept mail from me.

I use a fat mail client (thunderbird) when I'm at home and a web based
one (horde imp) when I'm away. Thunderbird sends mail using my ISP's
smtp server, so from there I can send mail to hotmail and yahoogroups
just fine. When I'm away using the web based client, it uses sendmail
directly, and the mail sits in /var/spool/mqueue for five days until
it bounces. 'mailq' shows:

                /var/spool/mqueue (1 request)
-----Q-ID----- --Size-- -----Q-Time-----
------------Sender/Recipient-----------i5S8v2K3018352     2893 Mon Jun
28 09:57 <my at address.com>
                 (reply: read error from mx1.hotmail.com.)
                                         <addressee at hotmail.com>
                Total requests: 1

What I want to know is this: what do I have to do to sendmail.mc to
get sendmail to do as thunderbird is doing and just talk smtp to my
ISP's smtp server for remote delivery, but carry on doing what its
doing now for local delivery?

Cheers,

Eliot.