To enable Auto-reply on E-mail address in the plesk control panel, please follow the following steps :-
1) Login to Plesk Control Panel.
2) Click on "Mail Tab" and click on "E-mail Address".
5) Click on Auto-Reply Tab and then "Enter the following details :-
6) Once you have entere the above details click on "OK" and email account will be configured.
For Flash Tutorial : Click Here.