Install dovecot IMAP server on RHEL7

# Add firewall services for mail submission, imap
sudo firewall-cmd --permanent --add-service={smtp-submission,smtps,imap,imaps} 
# Reload firewall
sudo firewall-cmd --reload
# Verify services
sudo firewall-cmd --list-services 

sudo certbot certonly -a nginx --agree-tos --staple-ocsp --email you@example.com -d mail.yourwebsite.com

# You should have new certs generated for your mail host under /etc/letsencrypt folder, will use those certificates for later steps.

sudo vi /etc/postfix/master.cf
# Update blow lines
submission     inet     n    -    y    -    -    smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_security_level=encrypt
  -o smtpd_tls_wrappermode=no
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
  -o smtpd_recipient_restrictions=permit_mynetworks,permit_sasl_authenticated,reject
  -o smtpd_sasl_type=dovecot
  -o smtpd_sasl_path=private/auth

smtps     inet  n       -       y       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
  -o smtpd_recipient_restrictions=permit_mynetworks,permit_sasl_authenticated,reject
  -o smtpd_sasl_type=dovecot
  -o smtpd_sasl_path=private/auth

#Enable TLS Encryption when Postfix receives incoming emails
smtpd_tls_cert_file=/etc/letsencrypt/live/mail.your-domain.com/fullchain.pem
smtpd_tls_key_file=/etc/letsencrypt/live/mail.your-domain.com/privkey.pem
smtpd_tls_security_level=may 
smtpd_tls_loglevel = 1
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache

#Enable TLS Encryption when Postfix sends outgoing emails
smtp_tls_security_level = may
smtp_tls_loglevel = 1
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

#Enforce TLSv1.3 or TLSv1.2
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtpd_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtp_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1

sudo systemctl restart postfix

sudo ss -lnpt | grep master

# Run below command to install dovecot
sudo yum install dovecot

# Check installed version
dovecot --version
# Enable dovecot service and start dovecot
sudo systemctl enable dovecot
sudo systemctl start dovecot 

# Check dovecot is running
sudo systemctl status dovecot
# Example output
● dovecot.service - Dovecot IMAP/POP3 email server
   Loaded: loaded (/usr/lib/systemd/system/dovecot.service; enabled; vendor preset: disabled)
   Active: active (running) since Fri 2021-12-31 14:16:13 AST; 22s ago
     Docs: man:dovecot(1)
           http://wiki2.dovecot.org/
  Process: 20906 ExecStart=/usr/sbin/dovecot (code=exited, status=0/SUCCESS)

sudo vi /etc/dovecot/dovecot.conf

# Change protocols you want to enable.
protocols = imap lmtp

# Update mail location, edit /etc/dovecot/conf.d/10-mail.conf file
sudo vi /etc/dovecot/conf.d/10-mail.conf
# Find and update below line
mail_location = maildir:~/Maildir
# Add below line in the file
mail_privileged_group = mail

# Save and close this file, then add dovecot to mail group in order to read emails
sudo gpasswd -a dovecot mail

# Update /etc/dovecot/conf.d/10-master.conf file
sudo vi /etc/dovecot/conf.d/10-master.conf 
# Update lmtp service configuration
service lmtp {
 unix_listener /var/spool/postfix/private/dovecot-lmtp {
   mode = 0600
   user = postfix
   group = postfix
  }
}
# Save and close file.

# Update main configuration /etc/postfix/main.cf
sudo vi /etc/postfix/main.cf
# Adding below lines to end of this file
mailbox_transport = lmtp:unix:private/dovecot-lmtp
smtputf8_enable = no

# Update /etc/dovecot/conf.d/10-auth.conf file
sudo vi /etc/dovecot/conf.d/10-auth.conf
# Find and update below lines:
disable_plaintext_auth = yes
auth_username_format = %Lu
auth_mechanisms = plain login

# Save and close file

# Update /etc/dovecot/conf.d/10-ssl.conf file
sudo vi /etc/dovecot/conf.d/10-ssl.conf
# Find and update below lines:
ssl = required
ssl_prefer_server_ciphers = yes
# Update certs file
ssl_cert = </etc/letsencrypt/live/mail.yourwebsite.com/fullchain.pem
ssl_key = </etc/letsencrypt/live/mail.yourwebsite.com/privkey.pem
# Save and close file

# Uncomment below line
#ssl_dh = </etc/dovecot/dh.pem
#ssl_min_protocol = TLSv1.2

sudo openssl dhparam -out /etc/dovecot/dh.pem 4096

sudo vi /etc/dovecot/conf.d/10-master.conf
# Find and update below lines:
service auth {
    unix_listener /var/spool/postfix/private/auth {
      mode = 0600
      user = postfix
      group = postfix
    }
}
# Save and close file

sudo vi /etc/dovecot/conf.d/15-mailboxes.conf
# Find and update below lines, same rules can be applied to Drafts, Junk, Trash and Sent folders
mailbox Trash {
    auto = create
    special_use = \Trash
}
# Save and close file

sudo systemctl restart postfix dovecot

# Check ports dovecot is listening
sudo ss -lnpt | grep dovecot

dd if=/var/lib/dovecot/ssl-parameters.dat bs=1 skip=88 | openssl dhparam -inform der > /etc/dovecot/dh.pem

openssl dhparam -out /etc/dovecot/dh.pem 4096 -days 3650