In Outlook 2007 and I am sure in older versions as well, you can set your own delivery options.
Read receipt and delivery receipt is standard, but have to delay sending emails and have them expire after few days is definitely cool and useful.
I am sure you can think of some situations in which you can delay sending emails – even to yourself as a reminder to your personal email address like yahoo, windows live hotmail or gmail accounts.
Can you think of a situation in which you would like to expire your email? I use this option a lot, especially when I am sharing product keys with colleagues. I am email them product keys and then set them to expire in 30 minutes. As a courtesy, I inform them verbally that I have set this option and the email won’t stay for long. In my sent items, when the email has expired, it will show as can be seen.
This is really handy. Can you think of any other situations?