Do this when your planning to be out of the office for any duration of time.

Outlook Desktop Client

Click File > Automatic Replies.
Select the Send automatic replies radio button.
If you want the automatic replies to be between a certain time frame check off the Only send during this time range.
Ensure to record a message for either inside or outside organization or both.
If, for example, you want certain individuals emails or emails with certain subjects not to receive the automatic reply, click Rules… > Add Rule…
Create the rule and choose what you want it to do instead.
Click OK.

Outlook Web Version

Go to https://connect.uwaterloo.ca/owa and login with your WatIAM username (e.g., cw-tech) and its associated password.
Click the cog icon in the top-right corner and choose Options.
Under Mail > Automatic processing > Automatic replies, choose Send automatic replies and then type the message to be sent when people email your account in the text box.
Check or uncheck Send replies only during this time.
Check or uncheck Send automatic reply messages to senders outside my organization.
Click Save.