Solved

How to TELNET

Posted on 2004-10-28
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Last Modified: 2010-04-14
Dumb ass question ...

From a Windows 2003 DC, (or any desktop come to that), why can I not 'TELNET mymailserver 23/25' ?

I get 'Could not open connection to host: Connection failed'

Any obvious reasons ?

I'm looking to test SMTP connectivity ...

Thanks

S.S.
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Question by:SpencerSteel
    16 Comments
     
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    Expert Comment

    by:Debsyl99
    Hi

    Have you tried just

    telnet yourmailserver 25

    Deb :))
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    Author Comment

    by:SpencerSteel
    yes ... the 23/25 thing was meaning I tried both ...

    I'm dim ... but not *that* dim :)

    S.S.x
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    LVL 20

    Assisted Solution

    by:Debsyl99
    Ho to:
    XFOR: Telnet to Port 25 to Test SMTP Communication
    http://support.microsoft.com/default.aspx?kbid=153119&product=exch2k

    If you try telnet server 23/25 - It's trying to connect on port 23 and it obviously can't - I beleive telnet uses port 23 itself,

    Deb :))
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    Author Comment

    by:SpencerSteel
    Thanks for that,

    It's failing on 25. It must be some sort of security thing (again) as I can telnet from another server, but not this one.

    If I find out why this machine can't - i'll let you know.

    Thanks Debs

    S.S.x
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    Expert Comment

    by:nihlcat
    You've tried both IP and name?  
    What about access restrictions?
    http://support.microsoft.com/default.aspx?scid=kb%3BEN-US%3B324285#16
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    Expert Comment

    by:Debsyl99
    lol - sorry SS - I KNOW you're not dim!!
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    Expert Comment

    by:scampgb
    Hi SpencerSteel,
    > It's failing on 25. It must be some sort of security thing (again) as
    > I can telnet from another server, but not this one.

    Just to be clear then - you can telnet to your mailserver from other machines, but you can't telnet from one specific machine on your LAN?

    There's probably "something" blocking it.  This could either be access control on the SMTP service on your server (what email server are you running?) or a firewall (probably software) on either the server or the PC you're testing from.

    Check what, if any, firewall software installed.  Don't forget about the in-built MS firewall (right click on the network connection in Control Panel> Network), and that many anti-virus applications have basic firewall functionality.

    Port 25 is used for SMTP, so it's that port you need to connect to.  Port 23, as Debsyl99 rightly said, is used for connections to the Telnet daemon/service.

    Does that help?
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    Expert Comment

    by:Julian Hansen
    Can you send mail to the SMTP server from the workstation you are having problems with?
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    Author Comment

    by:SpencerSteel
    Ah ha ! ...

    I can "TELNET myserver 25" from any non-XP/2003 Server machine (ie. 2000 Pro/Workstation)

    Must be some new port blocking - although I am not using XP2 Firewall Settings ... oddness ... I will look around.

    Thanks

    S.S.
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    Assisted Solution

    by:Julian Hansen
    SS,

    I imagine then you are not able to send mail from these workstations. If you can look to see what the SMTP server is for the mail client - it might be pointing to the local machine. Virus checkers like Norton have a mail proxy option - your mail client talks to a local SMTP proxy that then connects out - all other attempts to connect out are blocked. I would look for a locally installed firewall or proxy software.

    BTW Can you ftp out from these workstations or is that blocked too?

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    Author Comment

    by:SpencerSteel
    I can send mail all OK ... there is an Exchange Server on the

    "TELNET myserver 25" machine ...

    The reason I'm doing all this should be explained I guess ...

    I'm using some backup software (Arceserve) that can send mail SMTP Alerts, once I job has completed. It's not working. I've been asked to test the SMTP and the easiest way to do that is to use TELNET.

    All other functionality (mail/exchange etc) is working in the domain fine.

    I'm obviously overlooking something obvious - it has to be related to the the fact that the new '2003/XP' are being blocked, but the older machines are not. I use ISA Server as a gateway, but I honest don't think that has anything to do with it - as I have one generic rule.

    It's not mission critical ... it's just very frustrating :)

    Thanks

    S.S.
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    Accepted Solution

    by:
    julianH,
    You said that you use ISA as a gateway.  Does traffic have to pass through the ISA gateway to get from the XP machine to "myserver"?
    If not, you can rule that out.

    From what you said, it's probably something on the client machine.  Check again for any firewalls (like the MS one).  Do you have any anti-virus software on the machine?


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    Expert Comment

    by:Julian Hansen
    scampgb,

    I think you meant to address the previous post to SpencerSteel - he is the one having the problem. ;)

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    Expert Comment

    by:scampgb
    julianH: Oopsie - that's what happens when I'm not paying attention!


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    Author Comment

    by:SpencerSteel
    AH HA!!

    Thanks Julian,

    I remember that when I built these new machines, I put ni the the McAfee Virusscan 8.0i Enterprise, which I have just found, has Port Blocking rules. As part of the default installation, it creates a series of rules including one that blocks port 25 to stop mass mailer viruses.

    My god ... i've been running around in circles and it was *that* simple.

    I'll split these points up and skulk away again, feeling stupid. As usual.

    S.S.
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    Expert Comment

    by:scampgb
    Glad I could help :-)
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