To set your vacation message:

go to https://config.mail.yale.edu
log in with your netID and password
On the E-mail Auto-Reply (Vacation) line, click "Configure"
Enter the message you would like users to receive
Click "Activate"
Log out.

How it works:

This will set a vacation message that will send an automatic reply that you are out of the office or away.

Don't forget to deactivate your vacation message when you return.

Note that the vacation program keeps track of who it has replied to, only sending one reply per person per week. For example: If Jane sends an email on the 1st, the 2nd and then the 8th and 9th, she will get an automatic reply on the 1st and 8th, but not the 2nd or the 9th.