Posted by on 01 August 2012 03:40 PM
ETRN (Extended TURN) is SMTP protocol extension for on-demand mail relay with DNS resolution with fixed IP address. It can be used to release the load of the destination server by using a gateway to filter spam and viruses.
ATRN (Authenticated TURN) can be used when the destination server does not have a fixed IP address and/or is not permanently connected to Internet. It is more secure and recommended to be used.
The session is initiated by the destination server, which then issues ETRN or, after authentication, ATRN command. Both, "backup" server and client server need to be set up to use ETRN/ATRN.
The procedure of execution of this command is: destination server (client in this session, let's call it A) connects to the one (server in this session, let's call it B) that holds mail for it, issues ETRN or ATRN command, they exchange their roles so B becomes client and A becomes server. What follows is normal SMTP session with MAIL FROM commands etc. That means, all filters and antivirus are applied by destination server.
Backup Server Setup
The first step on the destination server setup is to create a domain and set its type to ETRN/ATRN queue domain in the combo box in the domain's properties on the Accounts tab. If ETRN will be used (destination server has fixed IP address), Value: field should contain this IP address. If the server has dynamic IP, leave this field empty as in the picture.
Then add one account to this domain which will be used for authentication by the destination server when asking for mail. Password is not mandatory if ETRN will be used, but if set, it will be required from the remote server.
Set this account to be an ETRN/ATRN account by checking ETRN/ATRN account checkbox on the Options tab (it would not work without this enabled)
This account's login information will be used by the destination server.
Now our ETRN/ATRN domain is ready and you can move to the next and final step – configuring the destination server.
Destination Server Setup
Go to Mail Service -> ETRN Download
Here create a new ETRN Download by clicking Add and defining the parameters.
Parameters field then contains what parameters should be passed with the ETRN command to the server. If password is required for the domain, it should be separated from the domain name by one space. In the case multiple ETRN commands should be passed to the server, separate parameters for each command by semicolon(s):
If ATRN needs to be used, check ATRN checkbox. Parameters for ATRN must be domain name followed by semicolon, login, colon and password.
Then just press OK button and, the final step, schedule execution of ETRN/ATRN session(s).