BEST: Tested and Worked

Part1: set up a basic Postfix SMTP server

Part2: receive and send emails using a desktop email client

Part3 (MySQL): Create Virtual Mailboxes on Ubuntu Mail Server

Part3 (Postgres): Create Virtual Mailboxes on Ubuntu Mail Server

Part4: DKIM and SPF

Part5: DMARK

Part6: Prevent being marked as spam

Postscreen

Postscreen

Block and antispam

Block and Filter

OpenDMARC

Multiple Domain

Multiple Mail Domains in PostfixAdmin

Postfix Admin

Install Postfix Admin

Roundcube

Install Roundcube

Postfix SendOnly

Set Up Postfix Send-Only SMTP Server on Ubuntu 22.04/20.04/18.04

queue mangement

# view the Postfix mail queue
sudo postqueue -p

# delete specefic message from queue
sudo postsuper -d msg_id

# delete all messages from the queue
sudo postsuper -d ALL

migrate to another let's encrypt certificate

add new one

sudo mkdir -p /var/spool/postfix/etc/letsencrypt/live/example.com
sudo cp /etc/letsencrypt/live/example.com/{fullchain.pem,privkey.pem} /var/spool/postfix/etc/letsencrypt/live/example.com/

# in main.cf
smtpd_tls_cert_file = /etc/letsencrypt/live/example.com/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/example.com/privkey.pem

flush postfix cache

sudo systemctl stop postfix
sudo rm -rf /var/spool/postfix/private/tlsmgr/*

dovecot

# edit the 10-ssl.conf
ssl_cert = </etc/letsencrypt/live/example.com/fullchain.pem
ssl_key = </etc/letsencrypt/live/example.com/privkey.pem

# remove ssl caceh (?) (possibly is not needed)
sudo systemctl stop dovecot
sudo rm -rf /var/lib/dovecot/ssl-parameters.dat

restart postfix and dovecot

sudo systemctl start postfix dovecot