bulk email

Hi, I'm working on a bulk (opt in!) email delivery system at the moment, and over the years I've heard a number of possibly apocryphal stories about people requiring contracts with large email suppliers (Hotmail, AOL, Yahoo, MSN etc..) in order to be able to guarantee delivery and lower the risk of email that's been requested by an end user being mistakenly blackholed or treated as spam by their ISP (or webmail provider). Has anyone ever actually come across such a contract in real life or are they just urban myths? Cheers, J.