A static IP is a must for Hotmail and many other mail servers like that.
Also make sure you have a valid SPF record, and that (in case of Hotmail) your domain(s) are added to the Hotmails SenderID program.
To get your domain(s) added to the SenderID program, you will need to contact Hotmail.
Please search this forum (keyword Hotmail) for more info.
A working fix might be to use you ISP's SMTP's server for sending mail.
Never execute code written on a Friday or a Monday.
Last edited by edge; 18th April 2008 at 22:13.