[exim] sending bulk mail

Is there a way to limit the rate of which Exim sends mail to each domain
name?

I run a service where my users can sign up to receive an email alert when
something matches their personal criteria. It's not spam, it really is a
valid service that my users pay me an annual fee to opt-in to the list.

When I blast thousands of emails to my users, I want them to get there as
quickly as possible. Exim does a great job of opening tons of outgoing
connections to as many SMTP servers that it can handle simultaneously.

My problem is, some domains detect dozens of incoming connections to their
SMTP servers from my one host, and start denying my connections thinking
that I'm a spam host.

For example, if I have 40 subscribers with Yahoo.com email addresses, the
first 5 emails will go through instantly, but each additional email will
be delayed a while due to remote SMTP errors, such as:

2006-02-05 02:16:13 1F5e84-0007Ze-LG SMTP error from remote mailer after initial connection: host mx1.mail.yahoo.com [4.79.181.14]: 451 mta185.mail.mud.yahoo.com Resources temporarily unavailable. Please try again later.

Other mail servers that do this are AOL.com, Verizon.com, Earthlink, and a
few others.

So I wonder, is there a way to limit the number of simultaneous
connections to each @domain name? Like if exim has 40 @yahoo.com
addresses in its outgoing queue, to wait for each one to send before
trying to send the next @yahoo.com mail?