Dovecot IMAP emails not saving?

Question

Mail server

Hi all!
There is an Ubuntu Server 16.04 system with a mail server (Postfix + Dovecot + MySQL)
The problem is that clients (ThunderBird) periodically do not want to save sent letters.
dovecot.log

Oct 09 11:29:15 imap([email protected]): Warning: autocreate plugin is deprecated, use mailbox { auto } setting instead

Oct 09 11:29:17 imap-login: Error: SSL: Stacked error: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48
Oct 09 11:29:17 imap-login: Info: Disconnected (no auth attempts in 0 secs): user=<>, rip=105.650.321.444, lip=45.450.126.360, TLS: SSL_read() failed: Unknown error, session=<PKKB/Bhb0iJbvlPS>
Oct 09 11:29:17 auth: Debug: auth client connected (pid=5850)
Oct 09 11:29:17 imap-login: Error: SSL: Stacked error: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48
Oct 09 11:29:17 imap-login: Info: Disconnected (no auth attempts in 0 secs): user=<>, rip=105.650.321.444, lip=45.450.126.360, TLS: SSL_read() failed: Unknown error, session=<rEiD/Bhb0yJbvlPS>

syslog

Oct  9 11:35:05 Ubuntu-1604-xenial-64-minimal postfix/pipe[6103]: .... doveconf: Warning: NOTE: You can get a new clean config file with: doveconf -n > dovecot-new.conf do))

dovecot-a

# 2.2.22 (fe789d2): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.13 (7b14904)
doveconf: Warning: NOTE: You can get a new clean config file with: doveconf -n > dovecot-new.conf
doveconf: Warning: Obsolete setting in /etc/dovecot/dovecot.conf:13: 'imaps' protocol is no longer necessary, remove it
doveconf: Warning: Obsolete setting in /etc/dovecot/dovecot.conf:13: 'pop3s' protocol is no longer necessary, remove it

dovecot config

spoiler

!include_try /usr/share/dovecot/protocols.d/*.protocol
listen = *
base_dir = /var/run/dovecot/
login_greeting = Dovecot ready.

dict {
  #quota = mysql:/etc/dovecot/dovecot-dict-sql.conf.ext
  #expire = sqlite:/etc/dovecot/dovecot-dict-sql.conf.ext
}

mail_location = mbox:~/mail:INBOX=/var/mail/%u
mail_privileged_group = mail
mail_location = maildir:/var/vmail/%d/%n
mail_uid = vmail
mail_gid = mail

disable_plaintext_auth = no
auth_mechanisms = plain login cram-md5
#!include auth-system.conf.ext
!include auth-sql.conf.ext

#IMAP
!include conf.d/*.conf
!include_try local.conf
protocols = pop3 pop3s imap imaps

protocol imap {
  # Space separated list of plugins to load (default is global mail_plugins).
  mail_plugins = $mail_plugins autocreate

  # Maximum number of IMAP connections allowed for a user from each IP address.
  # NOTE: The username is compared case-sensitively.
  mail_max_userip_connections = 1000
}

# At the end of file paste following code
plugin {
autocreate = Trash
autocreate2 = Junk
autocreate3 = Drafts
autocreate4 = Sent
autosubscribe = Trash
autosubscribe2 = Junk
autosubscribe3 = Drafts
autosubscribe4 = Sent
}

#default_process_limit = 100
#default_client_limit = 1000
#default_vsz_limit = 256M
#default_login_user = dovenull
#default_internal_user = dovecot

service imap-login {
  inet_listener imap {
    #port = 143
  }
  inet_listener imaps {
    #port = 993
    #ssl = yes
  }

  #service_count = 1

  # Number of processes to always keep waiting for more connections.
  #process_min_avail = 0

  # If you set service_count=0, you probably need to grow this.
  #vsz_limit = $default_vsz_limit
}

service pop3-login {
  inet_listener pop3 {
    #port = 110
  }
  inet_listener pop3s {
    #port = 995
    #ssl = yes
  }
}

service lmtp {
  unix_listener lmtp {
    #mode = 0666
  }

  #inet_listener lmtp {
    # Avoid making LMTP visible for the entire internet
    #address =
    #port = 
  #}
}

service imap {
  # Most of the memory goes to mmap()ing files. You may need to increase this
  # limit if you have huge mailboxes.
  #vsz_limit = $default_vsz_limit

  # Max. number of IMAP processes (connections)
   process_limit = 1024
}

service pop3 {
  # Max. number of POP3 processes (connections)
  #process_limit = 1024
}

service auth {
  unix_listener auth-userdb {
    #mode = 0666
    #user = 
    #group = 

    mode = 0666
    user = vmail
    group = mail
  }

  # Postfix smtp-auth
    unix_listener /var/spool/postfix/private/auth {
    mode = 0666
    user = postfix
    group = postfix
  }

  # Auth process is run as this user.
  #user = $default_internal_user
}

service auth-worker {
  # Auth worker process is run as root by default, so that it can access
  # /etc/shadow. If this isn't necessary, the user should be changed to
  # $default_internal_user.
  #user = root
}

service dict {
  # If dict proxy is used, mail processes should have access to its socket.
  # For example: mode=0660, group=vmail and global mail_access_groups=vmail
  unix_listener dict {
    #mode = 0600
    #user = 
    #group = 
  }
}

ssl = yes
ssl_cert = </etc/postfix/certs/cert.pem
ssl_key = </etc/postfix/certs/key.pem
# 
ssl_protocols = !SSLv2 !SSLv3
ssl_cipher_list = ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+3DES:DH+3DES:RSA+AESGCM:RSA+AES:RSA+3DES:!aNULL:!MD5:!DSS

postmaster_address = [email protected]

protocol lda {
  # Space separated list of plugins to load (default is global mail_plugins).
  #mail_plugins = $mail_plugins
}

#Логи
log_path = /var/log/dovecot.log
auth_verbose = yes
auth_debug = yes
mail_debug = yes

Answer 1

Warning: autocreate plugin is deprecated
unknown ca
'imaps' protocol is no longer necessary
Read the documentation for your version of dovecot. Do not stupidly copy-paste, or update without reading the ReleaseNotes. In the first case, you use an outdated plugin that does not create the necessary folders for the Thunderbird folder, in the second you did not specify the certificate of the certification authority, in the third the configuration file format has changed, and encryption is now specified in a different way.
And learn how to google.