[Exim] too many connections

Hello,

when I came in to my office today I was welcome with dozens of lines
like the following:

2004-01-29 12:44:28 Connection from 82.82.80.85 refused: too many
connections
2004-01-29 12:44:28 Connection from 80.3.248.196 refused: too many
connections
2004-01-29 12:44:39 Connection from 213.54.96.249 refused: too many
connections
2004-01-29 12:44:40 Connection from 82.82.80.85 refused: too many
connections
2004-01-29 12:44:44 Connection from 195.71.116.194 refused: too many
connections
2004-01-29 12:44:51 Connection from 213.54.96.249 refused: too many
connections
2004-01-29 12:44:54 Connection from 80.129.253.57 refused: too many
connections
2004-01-29 12:44:54 Connection from 62.146.51.210 refused: too many
connections
2004-01-29 12:44:59 Connection from 80.138.179.8 refused: too many
connections
2004-01-29 12:45:00 Connection from 82.82.80.85 refused: too many
connections
2004-01-29 12:45:25 Connection from 217.232.31.26 refused: too many
connections

When I looked to the processlist with "pstree -p" and "ps ax", I could
see only 10 or 15 exim processes. When I tried to send a mail, I wsa
refused by

421 some.server.name: Too many concurrent SMTP connections; please try
again later.

I found some older posts on that, but nothing that told me the
background and the solution for this. I restarted exim and at least
until now, everything is fine again. But where does this error come
from? I'm using a really standard configuration-file. Is there a
directive to increase the allowed concurrent connections?

Regards
Marten