This article will describe installing Postfix as SMTP server and send mail to localhost and your domain. And then send mail to internet via Gmail.
Table of Contents
1 Send mail to localhost and your domain
- If you send mail to only localhost, set myhostname = localhost and mydomain = localdomain.
- If you send mail to your domain, set your hostname to myhostname and your domain to mydomain. This hostname and domain must be known with multiple machine (common /etc/hosts or DNS server). Both mail sender machine and receiver machine needs this Postfix setting.
The following script will set myhostname = localhost and mydomain = localdomain.
#!/bin/sh postfix_install() { cat <<EOF | sudo debconf-set-selections postfix postfix/main_mailer_type select No configuration EOF sudo apt install -y postfix # shellcheck disable=SC2016 cat <<EOF | sudo tee /etc/postfix/main.cf myhostname = ${1} mydomain = ${2} myorigin = \$myhostname.\$mydomain mydestination = localhost, localhost.\$mydomain, \$myhostname, \$mydomain, \$myorigin compatibility_level = 2 command_directory = /usr/sbin daemon_directory = /usr/lib/postfix data_directory = /var/lib/postfix mail_owner = postfix inet_interfaces = all local_recipient_maps = unix:passwd.byname \$alias_maps unknown_local_recipient_reject_code = 550 mynetworks_style = subnet mynetworks = 127.0.0.0/8 alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases smtpd_banner = \$myhostname ESMTP \$mail_name (Debian/GNU) debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin ddd \$daemon_directory/\$process_name \$process_id & sleep 5 sendmail_path = /usr/sbin/postfix newaliases_path = /usr/bin/newaliases mailq_path = /usr/bin/mailq setgid_group = postdrop inet_protocols = ipv4 EOF sudo newaliases sudo systemctl restart postfix sudo apt install -y mutt } postfix_main() { postfix_install localhost localdomain # localhost only. # postfix_install ${YOUR_HOSTNAME} ${YOUR_DOMAIN} # your network. } postfix_main
2 Send mail to internet via Gmail
You need the previous Postfix setting. The myhostname and mydomain can be localhost setting or your domain setting.
Append the following to /etc/postfix.main.cf.
$ cat <<EOF | sudo tee -a /etc/postfix/main.cf relayhost = [smtp.gmail.com]:587 smtp_sasl_auth_enable = yes smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd smtp_sasl_security_options = noanonymous smtp_sasl_mechanism_filter = plain smtp_use_tls = yes EOF
Create /etc/postfix/sasl_passwd. Please set your Gmail address to GMAIL_ADDR and your Gmail password to GMAIL_PASSWD.
$ echo "[smtp.gmail.com]:587 ${GMAIL_ADDR}:${GMAIL_PASSWD}" | \ sudo tee /etc/postfix/sasl_passwd $ sudo chmod 600 /etc/postfix/sasl_passwd $ sudo postmap hash:/etc/postfix/sasl_passwd
Restart Postfix.
$ sudo systemctl restart postfix
Gmail will return authentication error.
postfix/smtp ... SASL authentication failed; server smtp.gmail.com...
The 2-step verification and application password is better. But this article will use "Allow less secure apps: ON".
https://myaccount.google.com/lesssecureapps
If Gmail returns authenticaion error again, you need "Allow access to your Google account".
https://accounts.google.com/DisplayUnlockCaptcha
And then you can send mail to internet via Gmail. Mail's from address is your Gmail address.
postfix/smtp ... to=<yourgmail@gmail.com>,relay=smtp.gmail.com ...