If you email server supports Out of Office/Vacation, you may be able to configure it from Apple Mail. Perform a Command+Right Click on the Mail account in the left panel. There either will be an “Out of Office” category on the menu or there won't. If not, the following will help with Out of Office/Vacation configuration.
If you are using iCloud, login through the iCloud.com web interface. Select the Mail client. Select the gear icon in the upper right toolbar and choose Preferences. Choose the Vacation menubar item in the pop-up window. Don't forget to turn this off when you return. Logout of the iCloud website.
Login to gmail.com. Select the gear icon > Settings. Under Settings > General, scroll down until you find the Vacation responder. Configure as needed. Logout.
There is more information at this previous Apple Support Community discusssion.