Proxmox Mail Gateway (PMG) routes all mails via the locally assigned IP addresses by default. This is usually only 1 IP address. Should you want to send mails in a round robin fashion using a number of IP addresses, you can follow this guide: https://base64.co.za/postfix-ip-rotation-for-proxmox-mail-gateway/.
If, for example, you want to route hotmail.com, outlook.com or live.com via another SMTP relay, you can follow this guide.
First and foremost you have to install the LibSASL module:
sudo apt install libsasl2-modules
Comment out transport_maps in /etc/pmg/templates/main.cf.in and add the following in it’s place:
transport_maps = regexp:/etc/postfix/transport.microsoft
Add the following at the bottom of that file:
# outbound relay configurations smtp_sasl_auth_enable = yes smtp_sasl_password_maps = hash:/etc/pmg/sasl_passwd smtp_sasl_security_options = noplaintext, noanonymous smtp_tls_security_level = may header_size_limit = 4096000
Edit transport.microsoft with:
Paste the following in that file:
The above simply routes outlook, hotmail, live, and msn domains via the SendInBlue SMTP relay.
Save and close that file and create the db file with the following:
Create the file that will contain the authentication credentials required to use the SMTP relay (Sendinblue):
Paste your credentials in as follows:
Save and close this file, and then generate the hash db as follows:
cd /etc/pmg/ systemctl restart postfix
Restart PMG with the new config:
pmgconfig sync --restart 1
Finally, change the permissions of the db file with the following:
chmod 0600 /etc/pmg/sasl_passwd /etc/pmg/sasl_passwd.db
You’re all done, and now all domains specified in the regex of the transport.microsoft file will be routed via the specified SMTP relay.