Mail and Telnet time out specially under Linux

[Ulrich Sucker <us@oceanmedia.de>]

Hi folks!

During debugging a mail problem, I found a very interesting problem.
My mail server says "connection timed out" if he tries to connect to
some specific systems which are properly run under windows. 
I tried to connect the system via telnet and telnet timed out also.
Then I tried some other machines (DOS, Windows, OpenBSD, SUN) and I
found only Linux machines with such kind of problems, but not all
Linux machines have this problem.
The problem depends not to the kernel version (we tried 2.2.xx, 2.4.18
- 24).

 I have problems with these machines:

213.160.64.50
149.201.40.50
212.223.86.31

Has anybody an idea?

Regards Uli