Out of office Rule

To set up an out of office message using a rule click File then Manage rules & alerts menu

then create a new Rule

Select Apply rule on messages I receive

Select Where my name is in the To box:

then select Have server reply using a specific message, then click the blue hyperlink to bring up the message template, type out your message and subject line then click save and next:

Now you can add some exceptions so that the rule doesn't reply to other automatic reply emails, make sure to tick the "except if it is an automatic reply" so the rule doesn't reply to other automatic messages 

then name the rule, switch it on and it will start replying to any new emails just remember that it will need manually switching off when not required and you won't get the warning message like with the inbuilt automatic reply option