Have you ever had to create a second account on a website, but you've only got one email address? I know I've had this problem when I've needed to create accounts for my sons (who aren't yet using their own email addresses).
There’s a way around this. Most web-based mail services allow you to create email aliases. When you use these email aliases any mail to that address is still delivered to your normal email address.
GmailFor Gmail addresses, you can add a +suffix to your email address. Only the characters up until the first plus sign are used to determine where the mail is delivered. For instance, emails sent to firstname.lastname@example.org and email@example.com will both go to firstname.lastname@example.org. If doesn't matter what the suffix is – +childsname, +shopping etc.
There is nothing you need to do to set up one of these alias email addresses - just type it when you need it. You can keep using it or not - and there's nothing to delete either.
Outlook.com (replaced Hotmail)
Open the options screen and click Create an Outlook alias. Email sent to the alias will appear in your normal Outlook.com email inbox. You can keep this address and use it or delete the alias later to prevent further emails from arriving.
The Outlook.com alias feature is even more useful than the Gmail option, because you can create a completely different email address, which you can use to send and receive emails. For example, a primary account of email@example.com could also have aliases of firstname.lastname@example.org, email@example.com, or any other variation (as long as that email address hasn't already been taken). Or, how about creating different addresses for different purposes: firstname.lastname@example.org, email@example.com.
Can you think of an instance where a second (third, fourth...) email address could have been useful to you?