confused with ssl settings and some error - need help

[Poliman - Serwis]

Hi,
To default dovecot.conf file I added (based on found documentation):
ssl = required
disable_plaintext_auth = yes     #change default 'no' to 'yes'
ssl_prefer_server_ciphers = yes
ssl_options = no_compression
ssl_dh_parameters_length = 2048
ssl_cipher_list =
ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA

1. Are these settings good or can be improved?
2. Is this line proper:
ssl_protocols = !SSLv2 !SSLv3 !TLSv1 !TLSv1.1
or maybe should be:
ssl_protocols = !SSLv2 !SSLv3
3. Last thing. I have below errors (they appear in loop in mail.err log
file):
#Apr 25 14:08:09 serwer-1 dovecot: imap-login: Error: SSL: Stacked error:
error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol
#Apr 25 14:08:09 serwer-1 dovecot: imap-login: Error: SSL: Stacked error:
error:1408A10B:SSL routines:ssl3_get_client_hello:wrong version number
#Apr 25 14:08:51 serwer-1 dovecot: imap-login: Error: SSL: Stacked error:
error:1408F119:SSL routines:SSL3_GET_RECORD:decryption failed or bad record
mac
#Apr 25 14:08:51 serwer-1 dovecot: imap-login: Error: SSL: Stacked error:
error:1408A0C1:SSL routines:ssl3_get_client_hello:no shared cipher

When I setup in postfix main.cf file (other lines default):
tls_ssl_options = no_ticket, no_compression
tls_preempt_cipherlist = yes
smtpd_sasl_security_options=noanonymous,noplaintext
smtpd_sasl_tls_security_options=noanonymous,noplaintext
smtpd_tls_mandatory_ciphers = high
smtpd_tls_dh1024_param_file = /etc/postfix/dh2048.pem
#instead of below I tried smtpd_tls_mandatory_exclude_ciphers but I don't
know what should be setup
smtpd_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK,
aECDH, EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CBC3-SHA, ECDHE-RSA-DES-CBC3-SHA,
DES-CBC3-SHA, RC4-MD5, RC4-SHA, ECDHE-RSA-RC4-SHA
smtp_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK, aECDH,
EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CBC3-SHA, ECDHE-RSA-DES-CBC3-SHA,
DES-CBC3-SHA, RC4-MD5, RC4-SHA, ECDHE-RSA-RC4-SHA

Is between dovecot and postfix some communication using above ciphers or
something that generate that errors in log or maybe some public client try
connect and can't establish connection?

Server with Ubuntu 16.04 LTS, postfix 3.1 and dovecot 2.2.22 and openssl
1.0.2k.
-- 

*Pozdrawiam / Best Regards*
*Piotr Bracha*




*tel. 534 555 877*

*serwis at poliman.pl <serwis at poliman.pl>*