What happens when...

you're going to be Out Of The Office so you set up an Autoreply on your Email Inbox to automatically email people who send you emails to let them know you're going to be Out Of The Office...then just to make sure it's working you send yourself a test email.

What happens is your email program receives your test email, then sends the sender an email to notify them that you're going to be out of the office, but you're the sender, so your email program sends you the notice. When that Out of Office Autoreply arrives in your Inbox, what happens? Oh yeah, your email program says "Hey! Another new Email! Send that Sender an Out of Office Autoreply!" So it does, and it sends itself another Out of Office Autoreply.

If the programmers who wrote your email program were smart they allowed for this eventuality, and your email program will realize what's happening after the 2nd or 3rd email it receives from itself and it will stop Autoreplying. If the programmers were not smart...well...I'd hate to see the results of the email bomb that you inadvertently sent yourself.