Spammers sometimes use automated programs to create Microsoft Outlook or other email accounts and then send junk email to others. That's why you're prompted to verify your account when you try to send an email message from Outlook for the first time.

When you click the verification link, you're asked to type a series of random characters as shown in a picture. (You can listen to an audio file that states the characters if you prefer.)

By entering the characters as shown, you prove that you're a human, and not an automated program. Outlook will occasionally prompt you to verify your account again, just to make sure you're still you and your account hasn't been compromised by spammers.