SubVS.co.uk

Its really useful to have a backup mail server if you receive smtp connections directly. Postfix can do this very easily, and takes minutes to set up. You could get a vps cheaply somewhere and set it up with just postfix and save yourself a lot of trouble if your main mail server goes down.

Forwarding mail server

First we add the realay_domains parameter, and then add the domains we want to relay. This tells postfix which domains it should relay (replace {yourdomain.com} with each domain that postfix should forward.

sudo echo "relay_domains = /etc/postfix/relay" >> /etc/postfix/main.cf

Repeat the following for each domain you want to forward:

sudo echo "{yourdomain.com}" >> /etc/postfix/relay

You now have a forwarding setver, you can test this by logging in with telnet to port 25, and sending a mail to the domain you want to back up. It will use DNS to find the primary MX, and send the mail there.

Forward to specific servers

If you prefer to specify the server to forward to, and ignore MX records in DNS (this was more useful for me), you can specify transport maps in your main.cf. This tells postfix that domains for xyz should be sent to the server at address abc.

sudo echo "transport_maps = hash:/etc/postfix/transport" >> /etc/postfix/main.cf

Now postfix knows where to look for the transport map, we populate it. Repeat the following line for each domain you want to specify a server to forward to (replace {hosttoforwardto} with the fqdn or ip address of the primary MX):

sudo echo "{yourdomain.com} smtp:{hosttoforwardto} >> /etc/postfix/transport 

Now make a hashed lookup table of the transport map we just made

sudo postmap /etc/postfix/transport

Finally, reload the postfix config

postfix reload

Bookmark/Search this post with: