Can't telnet to Postfix SMTP server after adding smtpd_sasl_auth_enable option

Question

I have the Postfix SMTP server installed on my CentOS 7 machine on port 25.
To test that it's working, I connect to it using telnet, like this:

# telnet localhost 25

and the result is:

Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 example.app ESMTP Postfix
EHLO test.com
250-example.app
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
quit
221 2.0.0 Bye
Connection closed by foreign host.

Which means it's working fine.
But now, in Postfix's config file /etc/postfix/main.cf I add the line:

smtpd_sasl_auth_enable = yes

Then I postfix reload and try the telnet connection again. And the result is:

Trying ::1...
Connected to localhost.
Escape character is '^]'.
Connection closed by foreign host.

The connection is closed automatically without receiving the 220 banner line.

I don't understand why it doesn't work. I've read the entire SASL README page at postfix.org and it says nothing about smtpd_sasl_auth_enable having this effect.

Why is telnet unable to establish a connection in this case and how can it be solved?

Please add your complete `main.conf`. It's not the `smtpd_sasl_auth_enable = yes` itself, but it enables the functionality, causing some other parameter to cause the problem. — Esa Jokinen, Jul 05 '19 at 05:40

score 2 · Answer 1 · answered Jul 05 '19 at 05:47

I found the problem so I guess I'll answer my own question.

The SASL library was missing the component cyrus-sasl-plain.

I installed it with yum install cyrus-sasl-plain and problem solved.

More info in this other question: POSTFIX fatal: no SASL authentication mechanisms

Can't telnet to Postfix SMTP server after adding smtpd_sasl_auth_enable option

1 Answers1