Gmail is set up to create a new contact for each e-mail you send. However, there are times when this can be more of a hassle than a handy tool. For instance, if you are replying to a lot of Craigslist ads for different pieces of furniture to put in your new apartment, your contacts list will likely get cluttered with nonsense e-mail addresses. Luckily there is an easy option that you can readily toggle off and on to control this feature of Gmail. Here's how:
Step 1: Log in to Gmail.
Step 2: Open the "Mail settings" menu at the top right (click on the gear icon).
Step 3: On the General tab, scroll down to "Create contacts for auto-complete."
Step 4: Choose whether you want Gmail to add contacts automatically (the default option), or will add them yourself.
Step 5: Press Save Changes at the bottom, and you're done.
Now you can send e-mail to anyone without worrying that you'll have a ridiculous number of unassigned e-mail addresses making a home in your contacts list. You can still find these addresses by checking the messages in your Sent mail area, so they're not too far out of reach should you need to find one of them again.