Cannot reach certain mail servers

Ed Greshko Ed.Greshko at greshko.com
Wed Nov 24 02:34:15 UTC 2004



Sysadmin wrote:
> 
> I have recently noticed a growing problem and am curious if anyone else
> is seeing the same.  There are certain email servers that I am not able
> to reach.
>   I get a "read timeout error"  I used the standard 'telnet mailhost 25`
> to troubleshoot and found that I am able to reach certain site just
> fine.  That being I get the RFC required banner.  While others I get
> nothing. It started out as some .gov sites (e.g. fernald.gov). But now
> we are unable to reach AOL.com as well.
>   I have even gone as far as looking at the packets with a sniffer.  I
> DO find differences.  The response coming back is different.
>   The REAL kicker is that the results vary by OS and connect type, 
> 
> RH8 - LAN connection - doesn't work here but does in another geographic
> location
> Windows XP - LAN - 2 different locations - doesn't work
> Windows XP - Dialup - works
> MAC OSX - LAN - Location 2 - works
> 
> The server used for the test case is running Sendmail 8.1.??.  I am
> running postfix 2.0.19 on Redhat 8.
> 
> Anybody seeing this or have any ideas.

Seeing this?  No.

Ideas?  Yes.

It has nothing to do with the O/S.  Most likely it has to do with the IP 
address of your systems and the related, or lack of, DNS information.

The receiving SMTP servers are most likely doing DNS and reverse DNS 
lookups.  If your systems are not fully registered in DNS there is a 
fair chance some systems will either timeout or refuse connections.

Regards,
Ed


-- 
"I think the problem, to be quite honest with you, is that you've never
actually known what the question is."

--The computer "Deep Thought" in "Hitchhiker's Guide to The Galaxy"




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