[Exim] How to deal with Hotmail

I have a difficult problem on one of my exim servers. Hotmail accepts
mail coming from my users, but the mail never gets delivered. It just
gets blackholed. The server isn't listed on any public DNSBL's, but it
is serving from DSL (SBC). The other server, which runs the same
version of exim, is also on DSL, but it is on Speakeasy.

My two best guesses as to what's going on are:

1) Hotmail has a problem with the SBC DSL server having a different
reverse DNS lookup (the IP resolves to
adsl-66-122-112-170.dsl.snfc21.pacbell.net. but the forward resolves to
dina.mrtoads.com.)

If this was the case, wouldn't the Hotmail server issue some complaint
and refuse the mail?

2) Hotmail decided to block SBC DSL IP's, but not Speakeasy DSL IP's.
This would seem to be a bit weird, but perhaps they have had spam
trouble from SBC.

Does anyone have any insight into the mysterious and annoying workings
of Hotmail?