we are running ESXi 4 and have some VMs installed. One is a Linux (CentOS 5.3) and one is a Windows 2003 server.
The Linux machine cannot send email to a remote Exchange server. The Windows server has no problems.
When using telnet on the Linux machine to port 25 on the remote server, it connects, but hangs on the line: escape character is ].
After some Enters, the welcome message from Exchange mailserver is shown and the HELO command etc. can be entered.
The windows server connects immediately to the mailserver and displays the message.
Also when sending a mail to a recipient on the exchange server through EXIM commandline, this generates a timeout. (another linux server in the same rack, not a VM, can send mail and telnet correctly to the remote server.). I also tested another exhcange mailserver and this one also generates a timeout. One more exchange server is connection as it should.
I tried disabling SELinux and IPtables. Even tried bypassing the hardware firewall. Also I have installed another Linux distribution. None of these have the desired effect.
ReverseDNS is working OK. Hostnames can be resolved. This all works.
Does anybody have an idea what to do next?