First of all, you need to install the application package. Next, you need to delete the standard settings files, since we will not use them in this project.

Installing the package:

doas pkg_add -v dovecot

Deleting standard configuration files:

cd /etc/dovecot/
doas rm -rf *

For the safe operation of the mail system, you need to create an additional user. We also create a folder for storing user mailboxes.

doas groupadd -ov -g 1100 mailman
doas useradd -v -d /var/spool/vmail -g 1100 -s /sbin/nologin -u 1100 -c "Mail man" mailman
doas mkdir -p /var/spool/vmail
doas chown mailman:mailman /var/spool/vmail

By default, resource limits are set for system services. But they are not enough for normal operation of the mail service, so you need to specify an additional value.

/etc/login.conf:

dovecot:\
	:openfiles-cur=1024:\
	:openfiles-max=2048:\
	:tc=daemon:

In this project, letters will be stored on the server disk in encrypted form. Therefore, you need to create encryption keys.

cd ~/
openssl ecparam -name prime256v1 -genkey | openssl pkey -out ecprivkey.pem
openssl pkey -in ecprivkey.pem -pubout -out ecpubkey.pem
doas mv ecprivkey.pem /etc/dovecot/ecprivkey.pem
doas mv ecpubkey.pem /etc/dovecot/ecpubkey.pem
doas chown _dovecot:_dovecot /etc/dovecot/ecprivkey.pem
doas chown _dovecot:_dovecot /etc/dovecot/ecpubkey.pem
doas chmod 600 /etc/dovecot/ecpubkey.pem
doas chmod 400 /etc/dovecot/ecprivkey.pem

doas touch /etc/dovecot/dovecot.conf

# Dovecot configuration file for my project

protocols = imap lmtp

mail_plugins = $mail_plugins quota mail_crypt

service imap-login {
  inet_listener imap {
    address = *
    port = 143
  }
  inet_listener imaps {
    address = *
    port = 993
     ssl = yes
  }
  user = _dovecot
  group = _dovecot
  executable = /usr/local/libexec/dovecot/imap-login
}

service auth {
  user = _dovecot
  group = _dovecot
  executable = /usr/local/libexec/dovecot/auth
}

service lmtp {
  unix_listener lmtp {
    mode = 0600
    user = mailman
    group = mailman
  }
  executable = /usr/local/libexec/dovecot/lmtp
}

service quota-warning {
  executable = script /usr/local/libexec/dovecot/quota-warning.sh
  unix_listener quota-warning {
    mode = 0600
    user = mailman
    group = mailman
  }
}

plugin {
  mail_crypt_global_private_key = </etc/dovecot/ecprivkey.pem
  mail_crypt_global_public_key = </etc/dovecot/ecpubkey.pem
  mail_crypt_save_version = 2
  quota = maildir:User quota
  quota_rule = *:storage=100M
  quota_rule2 = Trash:storage=+10M
  quota_max_mail_size = 10M
  quota_warning = storage=95%% quota-warning 95 %u
  quota_warning2 = storage=80%% quota-warning 80 %u
  quota_warning3 = -storage=100%% quota-warning below %u
}

quota_full_tempfail = yes

ssl = yes
ssl_cert = </etc/ssl/example.com.fullchain.pem
ssl_key = </etc/ssl/private/example.com.key
ssl_cipher_list = ALL:!LOW:!SSLv2

mail_location = maildir:/var/spool/vmail/%d/%n
mail_uid = 1100
mail_gid = 1100

valid_chroot_dirs = /var/spool/vmail

log_path = /var/log/dovecot.err
info_log_path = /var/log/dovecot.info
log_timestamp = "%Y-%m-%d %H:%M:%S "

login_greeting = Dovecot ready.

disable_plaintext_auth = no

auth_verbose = yes
auth_debug = yes
auth_debug_passwords = yes

auth_mechanisms = plain

passdb {
  driver = passwd-file
  args = /etc/dovecot/users.txt
}

In this project, notifications will be sent to the user when the quota chapel is reached. For this feature to work, you need to create an additional script.

doas touch /usr/local/libexec/dovecot/quota-warning.sh
doas chmod +x /usr/local/libexec/dovecot/quota-warning.sh

/usr/local/libexec/dovecot/quota-warning.sh:

#!/bin/sh

cat << EOF | /usr/local/libexec/dovecot/dovecot-lda -d $2 -o "plugin/quota=maildir:User quota:noenforcing"
From: admin@example.com
Subject: Quota warning

Your mailbox is now $1% full.
EOF

Next, you need to create a site with users, which will be used to authorize users in the system.

doas touch /etc/dovecot/users.txt

And we create our first user

doveadm pw -s BLF-CRYPT -u admin@example.com
<passwd>

/etc/dovecot/users.txt:

                                                                                                          
admin@example.com:{BLF-CRYPT}$2y$05$nigbXBiayNV/OaDAdS3aqOBlN.rcvkrOyfv6Y4QJl9RTT7jxA4sXC

doas chmod 640 /etc/dovecot/dovecot.conf
doas chmod 640 /etc/dovecot/users.txt

doas rcctl -d enable dovecot
doas rcctl -d start dovecot

doas rcctl -d start dovecot                     
doing _rc_parse_conf
doing _rc_quirks
dovecot_flags empty, using default ><
doing rc_check
dovecot
doing rc_start
doing _rc_wait start
doing rc_check
doing _rc_write_runfile
(ok)