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I want to send an email via telnet. When I typed to the command prompt 

telnet 'smtp_servername' 25 the following message appears
Could not open connection to the host, on port 25: Connect failed

Server name and listening port are correct. I have configured an account with these credentials with Mozilla Thunderbird (Secure Authentication: yes and Connection Security: None) and is working fine.

If I do the same test with the pop server is working fine.

telnet 'pop_servername' 110
+OK The Microsoft Exchange POP3 service is ready.

Any ideas why the smtp server is not answering my telnet connection?

Thanks in advance,

Albert

sysadmin1138
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Albert
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  • You should mark the answer that solved your issue as the correct answer by check-marking it. This will help future visitors of stackoverflow in faster finding the relevant piece of advice to their problem. – Oliver May 07 '13 at 10:43

2 Answers2

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Do you have a firewall that may block telnet.exe ? When using security, the tcp port often change from 25 to something else. Can you check that thunderbird didn't automatically changed the port number ?

When you do a telnet on a port, the other can't know it's telnet, until you type something at least (or timeout if you don't type fast enough)

Mathieu Chateau
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    If you know for a fact that the remote machine is running a SMTP server you probably have a firewall issue. Note that many ISPs now block port 25 to the outside world unless you're a "business customer", so the block may be outside your control. – voretaq7 Feb 08 '10 at 16:53
  • At the end was the firewall blocking. Thanks for the answers, the issue is finished, unfortunately due to the slow process of communication with the system IT department, I was unable to know the answer earlier. – Albert Feb 23 '10 at 08:45
  • Please mark this one as the answer then. – mlhDev Jan 25 '17 at 20:23
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You sure you did not set up the SMTP server to answer only to 'secure smtp' (port 465, IIRC)? This would explain the closed port 25.

Another hint: perhaps you need to authenticate first (via POP3) in order to have port 25 unblocked for your IP. Can you try telnetting after you successfully checked mail?

lorenzog
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