SSL problem - no banner

[Aki Tuomi]

> On May 29, 2017 at 9:27 PM Marcio Merlone <marcio.merlone at a1.ind.br> wrote:
> 
> 
> Hi,
> 
> I am running dovecot 2.2.22-1ubuntu2.4 on a ubuntu 16.04 server. It has 
> a valid Letsencrypt certificate but the problem also happens with a 
> self-digned one.
> 
> Only openssl s_client -connect localhost:993 works fine and fast, while 
> all MUA's and telnet does not. Telnet timeouts waiting for banner after 
> a minute or so:
> 
> root at netuno:~# openssl s_client -connect localhost:993
> CONNECTED(00000003)
> depth=2 O = Digital Signature Trust Co., CN = DST Root CA X3
> verify return:1
> depth=1 C = US, O = Let's Encrypt, CN = Let's Encrypt Authority X3
> verify return:1
> (...)
>      Start Time: 1496081321
>      Timeout   : 300 (sec)
>      Verify return code: 0 (ok)
> ---
> * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE 
> IDLE AUTH=PLAIN AUTH=LOGIN] Dovecot ready.
> 0 logout
> * BYE Logging out
> 0 OK Logout completed.
> closed
> 
> root at netuno:~# telnet localhost 993
> Trying 127.0.0.1...
> Connected to localhost.
> Escape character is '^]'.
> (about 1 minute later...)
> Connection closed by foreign host.
> root at netuno:~#
> 
> I Have enabled verbose_ssl = yes and mail_debug = yes but no useful info 
> got to logs. Has anyone seen this? Any hint?
> 
> Thanks, best regards.
> 
> -- 
> *Marcio Merlone*

It is not exactly obvious what you are expecting to happen. You won't get plain text banner out of port 993, if you want to use STARTTLS, use port 143.

Aki