Proxmox and Postfix SMTP Relay

This tutorial is going to show you how to set up Postfix SMTP relay on Proxmox VE 7.1 using Sendinblue (requires signing up for a free account). I have not tested this on earlier builds of Proxmox.

Install Postfix libsasl2-modules

apt install postfix libsasl2-modules

Once that’s complete, you will need to edit the main configuration file for Postfix.

nano /etc/postfix/main.cf

Add the following lines:

relayhost = [smtp-relay.sendinblue.com]:587
# outbound relay configurations
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

Then create the /etc/postfix/sasl_passwd file.

nano /etc/postfix/sasl_passwd

Add the following in the file:

[smtp-relay.sendinblue.com]:587 smtp_username:smtp_password

The SMTP_Username is the email address you used to sign up for Sendinblue. To get the password, you need to log in to Sendinblue and access SMTP & API settings under your user profile (Click on you username at the top right of the main Sendinblue page).

Then create the corresponding hash db file with postmap.

postmap /etc/postfix/sasl_passwd

Now you should have a file /etc/postfix/sasl_passwd.db. Restart Postfix for the changes to take effect.

systemctl restart postfix

By default, sasl_passwd and sasl_passwd.db file can be read by any user on the server. Change the permission to 600 so only root can read and write to these two files.

chmod 0600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db

Now we can send a test email with a command like below.

echo "this is a test email." | mailx -r from-address -s hello to-address

Please Note: Email may end up in your junk mail folder.