smtp service not responding to telnet locally

Posted on 2012-03-10
Medium Priority
Last Modified: 2012-03-31
I have about 10 domains all filtered thru our spam filter, all going to DIFFERENT exchange servers.   Something happend about 5pm yesterday that has cause 3 of the 10 to not receive mail any longer.

All have no windows firewall or other known firewall. No Antivirus / Malware software on them.  Very clean boxes.

Nothing has changed honestly on these boxes in years.  If you run telnet locally you get a flashing cursor not the typical header response.  I've restarted the services, made sure relaying was set appropriately etc.....

Question by:justingrantiv
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Expert Comment

ID: 37705804
Assuming you have tested whether you can access via telnet from a /different/ test machine to elimate that as the problem here are a few suggestions.

Has TLS/SSL been enabled (as a requirement) on the server inadvertantly?
Check the SMTP server settings.

have you used a dns lookup tool (for example the ones on the Demon.Net website) to validate you are actually connecting to the correct MX Relay address - somebody else might have changed it without your knowledge.

Are you definitely using "Telnet MachineHost 25" to specify the port correctly?
Try specifiying the server by IP rather than Hostname in case there is a typo/error etc and/or do a Ipconfig /flushdns.

Author Comment

ID: 37706091
TLS/SSL is not enabled i just double checked.  MX Relay is good and im using "telnet (machine name OR IP) 25"

Its totally strange this server has been functional for about 3 years no issues.  And what is even more strange is at about 5pm yesterday 3 of the 75 - 100 email servers we manage for clients are all doing the same thing.

From the console of the exchange server you can try to telnet server 25 and it will not respond directly on the server

Author Comment

ID: 37706159
tried changing the listening port from 25 to 587 and running telnet again.  No response from it on that port either.
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Expert Comment

ID: 37706675
there are so many variables server/network it is difficult to recommend things.

What kind of 'spam filter' is it?

Are the servers hosted off site - have you checked the hosting company hasnt changed their firewall policy? I know of lots of places that block outbound port 25 as they expect you to only relay mail through their servers, not direct from the server.

Have the bills been paid for the domain/server etc... this is easy to get caught out with.

the 'no answer on telnet' is more usually a sign of ssl - normally if you telnet to a closed/firewalled port telnet will refuse to connect, not sit there blank.

Make sure that the SMTP virtual server (service) is not stopped

Heres a more random test though, actually send some data through that session - e.g. typing
get / (newline)
to a port 80 connection will return a page from the server.
try typing
ehlo (newline)
to that correct port 25 connection

try an alternative, consider putty (search simon tatham) it is far superior to telnet in many ways and there are also different connection options within that that you can also try to use to determine your problem.

Accepted Solution

justingrantiv earned 0 total points
ID: 37767690
fixed by upgrading to a new exchange 2010 server.

Author Closing Comment

ID: 37790376
Fixed myself

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