[Exim] bulk email

Hi,

A bit off topic... but...

Forgive me if you saw my post on this topic to NANOG earlier today,
I got some useful replies there, but it just occurred to me that
this list will probably contain a number more people who have relevant
stories to tell in this area.

I'm working on a bulk (opt-in, verified subscription etc...) 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?

Other things I'm interested in is stuff like whether and how it's
necessary to rate limit sending to those domains, whether they
don't like single messages having more than a certain number of
RCPT TO lines, whether there are contracts that one can sign to
get access to some sort of super special non-public MX for them,
etc...

Cheers,

J.