Yes, there is a e-smith vacation add-on developed by Daniel van Raay. You can read more about that at
http://linux.made-to-order.net/Also, it's possible (but not recommended!) to install the vacation program for Qmail, edit the actual users ~/.qmail file and add the line
| /usr/local/bin/vacation username
to the bottom of that file.
Then you'll have to create a ~/.vacation.msg file.
I've done it and it works, but an add-on module would be preferable.