Two things with Hotmail and making it work.
(1) To even make it into Hotmail, you will
need a SPF record for the DNS / Domain.
If this is setup correct your email will endup in the users Bulk Mail
(2) To get the emails from your domain into the users Hotmail inbox, you will need
to contact the MSN / Hotmail postmaster with all the info asked here: http://advertising.msn.com/adproducts/email_bulkdupe
Once the postmaster is happy, they will 'white list' your domain.
PS. It's the same problem for Yahoo email addresses.