setup_linode_with_postfix.sh

#!/usr/bin/env bash

## Update
sudo apt-get update && sudo apt-get upgrade -y

## Update Hostname
echo "server" > /etc/hostname
hostname -F /etc/hostname

## Update hosts File
sudo mv /etc/hosts /etc/hosts.bak
touch /etc/hosts
cat > /etc/hosts <<EOF
127.0.0.1 localhost.localdomain localhost
45.33.1.26 server.default.systems server
45.33.1.26 mail.default.systems mail
2600:3c00::f03c:91ff:fec8:f546 server.default.systems server
2600:3c00::f03c:91ff:fec8:f546 mail.default.systems mail
# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
EOF

## Setup Postfix with Personal Gmail Account
HOST=$"mail.default.systems"

function install_postfix() {
echo | debconf-set-selections <<EOF
postfix	postfix/root_address	string	
postfix	postfix/rfc1035_violation	boolean	false
postfix	postfix/mydomain_warning	boolean	
postfix	postfix/mynetworks	string	127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
postfix	postfix/mailname	string	$HOST
postfix	postfix/tlsmgr_upgrade_warning	boolean	
postfix	postfix/recipient_delim	string	+
postfix	postfix/main_mailer_type	select	Internet with smarthost
postfix	postfix/destinations	string	$HOST, localhost.localdomain, localhost
postfix	postfix/retry_upgrade_warning	boolean

## Install postfix despite an unsupported kernel?
postfix	postfix/kernel_version_warning	boolean	
postfix	postfix/not_configured	error	
postfix	postfix/sqlite_warning	boolean	
postfix	postfix/mailbox_limit	string	0
postfix	postfix/relayhost	string	[smtp.gmail.com]:587
postfix	postfix/procmail	boolean	false
postfix	postfix/bad_recipient_delimiter	error	
postfix	postfix/protocols	select	all
postfix	postfix/chattr	boolean	false
EOF

echo "Postfix should be configured as Internet with smarthost"
apt-get install -q -y postfix mailutils libsasl2-2 ca-certificates libsasl2-modules zenity
}

if ! dpkg -s postfix >/dev/null;
then
  install_postfix
else
  echo "Postfix is already installed."
  echo "You may consider removing it before running the script."
  echo "You may do so with the following command:"
  echo "apt-get remove postfix --purge"
  echo
fi

if zenity --version >/dev/null; then
  GMAIL_USER=$(zenity --entry --title="Gmail username" --text="Enter your gmail username:")
  GMAIL_PASS=$(zenity --entry --title="Gmail password" --text="Enter your gmail password:")
else
  read -p "Gmail Username: " GMAIL_USER
  read -sp "Gmail Password: " GMAIL_PASS
fi

echo # an empty line

if [ -z "$GMAIL_USER" ]; then echo "No gmail username given. Exiting."; exit -1; fi
if [ -z "$GMAIL_PASS" ]; then echo "No gmail password given. Exiting."; exit -1; fi

if ! [ -f /etc/postfix/main.cf.original ]; then
   cp /etc/postfix/main.cf /etc/postfix/main.cf.original
fi

tee /etc/postfix/main.cf >/dev/null <<EOF
relayhost = [smtp.gmail.com]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_loglevel = 1
smtp_tls_per_site = hash:/etc/postfix/tls_per_site
smtp_tls_CAfile = /etc/ssl/certs/Equifax_Secure_CA.pem
smtp_tls_session_cache_database = btree:/var/lib/postfix/smtp_tls_session_cache
EOF

echo "[smtp.gmail.com]:587 $GMAIL_USER:$GMAIL_PASS" |  tee /etc/postfix/sasl_passwd >/dev/null
chmod 400 /etc/postfix/sasl_passwd
postmap /etc/postfix/sasl_passwd
echo "smtp.gmail.com MUST" |  tee /etc/postfix/tls_per_site >/dev/null
chmod 400 /etc/postfix/tls_per_site
postmap /etc/postfix/tls_per_site

service postfix restart
echo "Configuration done"
echo "Thank you for using this postfix configuration script." | mail -s "Email relaying configured at ${HOST}" $GMAIL_USER@gmail.com
echo "I have sent you a mail to $GMAIL_USER@gmail.com"
echo "This will confirm that the configuration is good."
echo "Please check your inbox at gmail."