It is not a tough task at all to set up an email auto-responder. For setting an auto-responder for your email account you first need to create a text file in your account which would be the body of the auto-responder. After you have created it you need to open that particular file and then create the body where the message of the auto-responder is written. Then you need to login to Webmin and there you need to substitute the name of the server with the name of the actual server that you are using for your account. Then you should go to the Servers section and then click on the Virtualmin Virtual Servers button. There under the Domain Name you should click on the domain name that you need to add the auto-responder to. Then on the Edit Server Page you need to go to the bottom and then click on Edit Mail and FTP Users button. Now you will be able to see all the mail users that are there in the particular domain.
In the next step you need to go to the Name button and then click on the name of the email user to whom you want to send your auto-responder. Now you need to send the auto-responder and for that you should go the Select box in the right of the Email forwarding destinations and there choose the Autoreply option from the file. In the field that is located beside the Select box you need to type the path of the auto-responder file.
If you want to receive the emails in this mailbox then you have to choose the option "This User's Mailbox" in the next Select box which is just under the first one and do not have to type anything in the corresponding text field. If this second option is not chosen then your mail will be responded and then will be deleted. Now click on the Save option so that the changes are saved