SSL problem - no banner

[Marcio Merlone]

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*