There are different answers, depending on what you are trying to do.
For Exchange email, you use the Out of Office Assistant via your email program. For details, see: How do I set an Out of Office (Automatic reply) message with Exchange Email?
Another possible solution is to set up a Mailman list and turn on the list's autoresponder.
Mailman lists have an auto-response built in, which you might be interested in testing. The functionality may not be what you want – you can customize the middle part of the autoresponse, but the beginning and end of the auto-response may not be configurable.
You can create a Mailman test list for yourself if you'd like to experiment with whether the Mailman auto-responder meets your needs. You can also ask the User Accounts office in the Computing Help Desk to create one for you.