1 Topic by tas.arturas

  • tas.arturas
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Topic: telnet to submission port(587) is dropped

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Hi,

why from one host connections to submission port(587) are dropped after initial greating?
We get "postfix banner", bet then connection is droped (we get RST packed).

From other hosts(other ISP) we got "postfix capabilities" and other responses and can "talk" with postfix (via openssl client).

Thank You
Arturas

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2 Reply by ZhangHuangbin

  • ZhangHuangbin
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Re: telnet to submission port(587) is dropped

Sorry, cannot help without related detail log. Please post log here so that others can help troubleshoot.

3 Reply by tas.arturas

  • tas.arturas
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Re: telnet to submission port(587) is dropped

In mail.log I see:
postfix/smtpd[27414]: connect from unknown[NN.NN.NN.NN]
postfix/smtpd[27414]: lost connection after CONNECT from unknown[NN.NN.NN.NN]
postfix/smtpd[27414]: disconnect from unknown[NN.NN.NN.NN]

As I wrote telnet to 25 works as expected, but to 587 is closed after initial greeting.
Wireshark on client side shows me TCP RST packet ir received...
This is for particular IP, not depending on OS, router.
Any ideas?

Thank You

4 Reply by ZhangHuangbin

  • ZhangHuangbin
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Re: telnet to submission port(587) is dropped

tas.arturas wrote:

As I wrote telnet to 25 works as expected, but to 587 is closed after initial greeting.

Telnet doesn't support TLS/SSL, so please use other tools for testing.

5 Reply by tas.arturas

  • tas.arturas
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Re: telnet to submission port(587) is dropped

I do know that telnet cannot handle TLS/SSL encryption, but problem is that Postfix(submission) on 587 port drops connection for particular clients (from same IP). From other IP's I can start telnet session on 587 port.
I know how to start "manual SMTP" session using OpenSSL client, but there is same "dropped connection" problem.

6 Reply by ZhangHuangbin

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Re: telnet to submission port(587) is dropped

Is this IP banned by iptables?