root@dovecot:~# uname -a
Linux dovecot 5.15.83-1-pve #1 SMP PVE 5.15.83-1 (2022-12-15T00:00Z) x86_64 GNU/Linux

# apt install dovecot-core dovecot-ldap dovecot-managesieved dovecot-sieve dovecot-imapd dovecot-antispam

# vi /etc/dovecot/dovecot-ldap.conf.ext

hosts = 2a02:8106:4:1800:cc20:a8ff:fe90:c2a0
base = ou=user,dc=grml,dc=de
ldap_version = 3
user_attrs = =user=%{ldap:uid}
user_filter = (&(objectclass=inetOrgPerson)(|(uid=%n)(mail=%u)))
pass_attrs = uid=user, userPassword=password
pass_filter = (&(objectclass=inetOrgPerson)(uid=%u))
auth_bind = yes
iterate_attrs = mail=user
iterate_filter = (objectclass=inetOrgPerson)
default_pass_scheme = SSHA

# vi /etc/dovecot/conf.d/10-auth.conf

[...]
auth_mechanisms = plain login
#!include auth-system.conf.ext
!include auth-ldap.conf.ext
[...]

# vi /etc/dovecot/conf.d/10-ssl.conf

[...]
ssl = required
ssl_cert = </opt/certs/grml.de/fullchain.cer
ssl_key = </opt/certs/grml.de/grml.de.key
ssl_dh = </etc/dovecot/dh.pem
ssl_min_protocol = TLSv1.2
ssl_cipher_list = ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384
ssl_prefer_server_ciphers = no
[...]

# openssl dhparam -out /etc/dovecot/dh.pem 4096
# doveadm user robin

field   value
uid
gid
home
mail    mbox:~/mail:INBOX=/var/mail/robin

# doveadm auth test robin P@ssw0rd

passdb: robin auth succeeded
extra fields:
  user=robin

# vi /etc/dovecot/conf.d/10-mail.conf

mail_uid = vmail
mail_gid = vmail
mail_privileged_group = vmail

mail_home = /home/vmail/mailboxes/%n
mail_location = maildir:~/mail:LAYOUT=fs

namespace inbox {
    inbox = yes
    mailbox Spam {
        auto = subscribe
        special_use = \Junk
    }
    mailbox Trash {
        auto = subscribe
        special_use = \Trash
    }
    mailbox Drafts {
        auto = subscribe
        special_use = \Drafts
    }
    mailbox Sent {
        auto = subscribe
        special_use = \Sent
    }
}

# useradd vmail
# doveadm user robin

field   value
uid     vmail
gid     vmail
home    /home/vmail/mailboxes/robin
mail    maildir:~/mail:LAYOUT=fs

# vi /etc/dovecot/conf.d/10-master.conf

[...]
service lmtp {
  inet_listener lmtp {
    # Avoid making LMTP visible for the entire internet
    address = 2a02:8106:4:1800:cc9f:11ff:fe0a:624f
    port = 24
  }
  user = vmail
}
[...]
service auth {
  unix_listener auth-userdb {
    #mode = 0666
    #user = 
    #group = 
  }
  inet_listener {
    port = 234
  }
}
[...]

# vi /etc/dovecot/conf.d/20-managesieve.conf

service managesieve-login {
  inet_listener sieve {
    port = 4190
  }
}