If you want to use Gmail for sending mails from postfix follow this guide.
First, install all necessary packages:
sudo apt-get install postfix mailutils libsasl2-2 ca-certificates libsasl2-modules
If you do not have postfix installed before, postfix configuration wizard will ask you some questions. Just select your server as Internet Site and for FQDN use something you like or if you have a FQDN; use that.
Add the following lines to /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_tls_CAfile = /etc/postfix/cacert.pem smtp_use_tls = yes
Create a new file /etc/postfix/sasl_passwd to store the Gmail credentials:
Note: If you want to use your Google App’s domain, just replace @gmail.com with your @yourgoogleappsdomain.com
Fix permission and update postfix config to use sasl_passwd file:
sudo chmod 400 /etc/postfix/sasl_passwd sudo postmap /etc/postfix/sasl_passwd
Next, validate certificates to avoid running into error. Just run following command:
cat /etc/ssl/certs/Thawte_Premium_Server_CA.pem | sudo tee -a /etc/postfix/cacert.pem
Restart your postfix server:
sudo /etc/init.d/postfix restart
Note: you can ignore errors like: warning: /etc/postfix/main.cf, line 43: overriding earlier entry: relayhost=
Test your setup with:
echo "Hello there, this is a test mail from postfix via Gmail." | mail -s "Test" email@example.com
If you run into troubles you probably are sending mail from a new IP of from a Gmail address that wasn’t used before.
In maillog you will find something like:
Error: “SASL authentication failed; server smtp.gmail.com”
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You can run test again after unlocking captcha.