Outlook - create a rule to automatically reply to new messages

You can create a rule to automatically reply to new messages under Outlook:

In Home tab go to Move and then click on Rules.
Click Manage Rules and alerts.
In the Rules and Alerts dialog, click New Rule.
Under Start from a blank rule, click on Apply rule on messages that I receive, and then click Next.

Down in window, click on the "a specific template" link and select the template of your choice.
Click on Next.
Set your exceptions (if needed) and settings.
Save your new rule and give a name to it.
Note that: For the Wizard to automatically sends a reply, Outlook must be enabled and configured to check periodically for new messages.
To create a message template, read Outlook - Create a message template.