General discussion



By alfonsoarias ·
I Have a Thunderbird Client installed in my destop. It has configured to send email using may email server on port 25, and it works fine: I can send emails .
But if I go to cmd, and try to do:
telnet email.server 25
Could not open connection to the host, on port 25: Connection failed.

My desktop uses XP, and the email server is a RedHat 3.0 Linux.

My PC uses as gateway a router, but in the router I have not restrictions, in fact I log in in my cisco router and I can telnet the email server send test emails with the command sequence EHLO/MAIL FROM/RCPT TO ... etc.

Why my PC can connect to email server on port 25 using thunderbird, but not using comand telnet ?

Thanks a lot.

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What does wireshark tell you ?

by thereallyniceman In reply to DSKTOP CAN'T TELNET TO EM ...

I suggest you load
and set a display filter for the mail server

and see what is happening when thunderbird contacts and when you telnet.

I suspect one or more of the following:
a) Thunderbird is using a secure port not the port 25.....

b) The XP (or other if you have it installed) firewall is blocking access on the basis of Port 25 or application+IP target of the mail server.

A final possibility is....
(especially if you cannot telnet as standard to the email server)
You are getting impatient, and not waiting (approx 2 mins) for the DNS on the linux box to timeout.... because there is no entry to match the host you are comming from.
Thunderbird is waiting, and getting there eventually.
If so, (as a quick fix) add an entry to the linux hosts file for the PC you are comming from.. it should resolve fast, and let you in quickly. A DNS entry can be added later if you are using a local DNS server.

Otherwise, come back with what wireshark is telling you about how far the telnet session gets in starting up..

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can't telnet email server on port 25

by alfonsoarias In reply to What does wireshark tell ...

1. I saw Thuderbird properties and its using port 25.
2. I started Windows Security Center (wscui.cpl) and Windows Firewall is Off (we are using Destktop Athoritty en our DC).
3. Is not DNS unresolved name, because when I ping email server it reponds immediatly.

What else can I check?

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Have you checked your AntiVirus software?

by GordonWatson In reply to can't telnet email server ...

Seen it with McAfee at least (especially if ProtectionPilot/ePo managed). The AV software will only allow certain apps to email so as to block mailing worms etc.

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What about pinging

by -Q-240248 In reply to DSKTOP CAN'T TELNET TO EM ...

Can you ping email.server and does it respond?

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Desktop is able to see email server

by alfonsoarias In reply to What about pinging

Yes, desktop is able to see the email server: if I ping it responds, and also thunderbird client its working: so it can connect with email server. Also, I saw in Thunderbird Properties and it is using email server on port 25 to send messages.

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by mveira In reply to Desktop is able to see em ...

Can the Linux server ping your machine? Does the same thing happen when a different computer tries to telnet to the Linux email server?
What antivirus/anti-spyware programs are installed on the desktop? Something could be blocking outgoing telnet connections but allowing the email client outbound access.

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McAfee seems to be the problem

by abisurd In reply to What about pinging

Reading your post, I ventured into McAfee's VirusScan Console. First item there is Access Protection. I opened it and immediately saw this item checked "Prevent mass mailing worms from sending mail". Port blocked is 25. There are a list of applications that are included in the excludes list. Items like Thunderbird.exe, outlook.exe etc are mentioned.

I tried adding cmd.exe to the list but that did not let me telnet to my smtp server's port. When I unchecked this protection item, I was able to telnet to the smtp port. I guess one needs to fiddle a little with it to be able to use the port even when this protection item is checked. I think unchecking it is an open invitation to mass emailing worms, in case you machine ever gets infected with one.

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