[Axxll]

How do I set my OSX 10.6.3 mail to auto reply when i am on holiday?

[AKcrab]

Check out the help in the mail app itself:

To automatically reply to messages:
1. Choose Mail > Preferences and click Rules.
2. Click Add Rule and type a descriptive name for the rule.
3. Set the conditions necessary for the rule to apply to a message.
4. From the “Perform the following actions” pop-up menu, choose “Reply to Message.”
5. Click “Reply message text” and enter the text for your reply message.

Mail will include the text you enter, along with the full text of the original message, in the message that it sends.

[besson3c]

That's going to require that you leave Mail open and constantly connected though, your Mac cannot go to sleep.

Auto-responders are best facilitated as server side mail rules, not client side ones.

[Big Mac]

You're right, but that is of course what he asked for.
I wish we could invent technology that would let us be able to stop writing email manually altogether.