[Exim] 421 Service not available

I've saw in my queue a message to that host...

i've activated debug:

Connecting to navgwnet.intnet.mu [202.123.2.2.25] ... connected

and exim waits and waits so on.

Then i've tryied manually:

[root@mta02 exim]# telnet navgwnet.intnet.mu 25
Trying 202.123.2.2...
Connected to navgwnet.intnet.mu.
Escape character is '^]'.
421 Service not available
Connection closed by foreign host.
[root@mta02 exim]#

Is that king of answer wrong?
Why exim doesn't report any error?

Thank you

Riccardo