Intermittent telnet connectivity issue to remote host port 25

view story

http://www.linuxquestions.org – I have an intermittent connectivity problem to smtp host in a remote windows machine. My application and email server are sitting in two diffrent data centers. First 4 to 5 connections are accepting and mails are going through email server. Connection is keep blocking for a short period of time from the same public IP. After few minutes its again allowing me to connect 3 or 4 times. Can someone please help me to identify the blocking issue..... Details : --------- Source Server : Ubuntu 12.04 LTS Destination Server : Windows 2008 R2 Destination Email Server : Hmail Server 5.3.3 port 25 T (HowTos)