[Exim] Error Message

I am not sure if the following error message is generated by Exim. If it is
not, please don't blast me with all sorts of abuse, just tell me.
The message I received is as follows:

"The TCP/IP connection was unexpectably terminated by the server. Server
response 421 (domain): Too many current SMTP connections, please try again
later."

Any help would be appreciated
If it helps, we are also running DNS on the same box - I know that DNS has
nothing to do with Exim.

Thanks