[exim] Slow down ?

Hi every body,
I've a problem with one of main French provider : orange.fr
When several messages are sent to @ orange.fr in a too short period of
time, they are (temporarily) refused:

> SMTP error from remote mail server after initial connection: 421
> mwinf5c78 ME Trop de connexions, veuillez verifier votre
> configuration. Too many connections, slow down. OFR004_104 [104]
The french part of this message say some thing like "Too many
connections, please verify you configuration"

Then the mailq takes a long time to empty ...

Well, the question in "how to slow down" ?

If I found the solution for Postfix, I did not find the one for exim :-(

Can you help me ?

Regards
Francois