In setting up my new mail server, I am getting the following in
      the logs:
    Oct 11 07:10:59 kumo dovecot[5704]: imap-login: Disconnected (no
      auth attempts in 0 secs): user=<>, rip=24.53.79.10,
      lip=172.26.12.90, TLS handshaking: SSL_accept() syscall
        failed: Success, session=<B9OokqCUD+UYNU8K>
    
    I have tried various ssl_protocols entries, but for now have
      defaulted back to ssl_protocols = !SSLv3 (the "out of the box"
      setting).
    The certificate (ssl_cert =
      </etc/ssl/certs/certificate_and_key.crt) is valid and the same
      one used by postfix.  However, I belive the error appeared only
      after removing the self signed certificate and installing the one
      I purchased.
    
    Warning:  though I was a sysadmin a long long time, it has been a
      while!  I have not run a mail server in 15 years, but am moving my
      mail back "in-house" as I approach retirement!  I searched for a
      forum where I could post this issue, but only found this list.
    
    
    
    
    
    # 2.2.33.2 (d6601f4ec): /etc/dovecot/dovecot.conf
    # Pigeonhole version 0.4.21 (92477967)
    # OS: Linux 4.15.0-1051-aws x86_64 Ubuntu 18.04.1 LTS 
    auth_mechanisms = plain login
    mail_location = maildir:~/Maildir
    mail_privileged_group = mail
    managesieve_notify_capability = mailto
    managesieve_sieve_capability = fileinto reject envelope
    encoded-character vacation subaddress comparator-i;ascii-numeric
    relational regex imap4flags copy include variables body enotify
    environment mailbox date index ihave duplicate mime foreverypart
    extracttext
    namespace inbox {
      inbox = yes
      location = 
      mailbox Drafts {
        special_use = \Drafts
      }
      mailbox Junk {
        special_use = \Junk
      }
      mailbox Sent {
        special_use = \Sent
      }
      mailbox "Sent Messages" {
        special_use = \Sent
      }
      mailbox Trash {
        special_use = \Trash
      }
      prefix = 
    }
    passdb {
      driver = pam
    }
    plugin {
      sieve = ~/.dovecot.sieve
      sieve_dir = ~/sieve
    }
    protocols = " imap sieve pop3"
    service auth {
      unix_listener /var/spool/postfix/private/dovecot-auth {
        group = postfix
        mode = 0660
        user = postfix
      }
    }
    ssl_cert = </etc/ssl/certs/certificate_and_key.crt
    ssl_cipher_list = ALL:!ADH:!LOW:!EXP:!aNULL:+HIGH:+MEDIUM
    ssl_client_ca_dir = /etc/ssl/certs
    ssl_key =  # hidden, use -P to show it
    userdb {
      driver = passwd
    }
    protocol lda {
      deliver_log_format = msgid=%m: %$
      mail_plugins = sieve
      postmaster_address = postmaster
      quota_full_tempfail = yes
      rejection_reason = Your message to <%t> was automatically
    rejected:%n%r
    }
    protocol imap {
      imap_client_workarounds = delay-newmail
      mail_max_userip_connections = 10
    }
    protocol pop3 {
      mail_max_userip_connections = 10
      pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
    }