SSL problem - no banner

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@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@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@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*