Can’t telnet to select mail servers; telnet session hangs (goes blank)

5 pts.
Tags:
Exchange 2003
Exchange 2003 administration
NDR
Network connectivity
Non-Delivery Reports
nslookup
Telnet
Windows Server 2003
Gents, I've an issue here that maybe some of you folks can help me with? I run a server 2003 shop with exchange 2003 (sp2). From time to time my users receive NDR's; see below for an example. Your message did not reach some or all of the intended recipients. Subject: RE: new e mail account Sent: 2/12/2009 8:41 AM The following recipient(s) cannot be reached: 'Jasper Darson ' on 2/14/2009 7:57 AM Could not deliver the message in the time limit specified. Please retry or contact your administrator. <ellsworth05.ellsworthbikes.com #4.4.7> The domain name is darson.com.tw, after doing an nslookup (q=mx), I get a mail server with the name "mail.darson.com.tw". From inside my companys network when I attaempt to connect via telnet (to test), the telnet session goes blank or hangs? It hangs not only from the exchange box but from any other server or wokrstation from inside the network? I can connect from home (or my personal exchange server) with no problems. Could the companies IP be blocked by this particular remote server? I have a handful of similar situtations. Please advise. -sna1alm

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That is a possibility. Have you been through the smtp logs on the exchange server to see what it shows you as the reason for the disconnect, like session was dropped, or session was disconnected or session rejected? Try getting the exchange admin for the receiving company on the phone if possible. They may be using a third-party filter like we do or they my not, but they can help identify the problem. Our third-party filter company restircts by IP and sometimes we have to get that corrected.

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Check your firewall rules. Be sure that port 25 outbound is permitted to all destination addresses unless you use a relay host. I have seen issues where one rule is applied to outbound traffic and a different rule to inbound traffic which means session state was lost. This effectively broke the 2-way conversation. You may need to do some packet snoops to capture exactly what is happening on both sides of the firewall to fully understand the issue.

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