Plus Addressing is a very simple way to have multiple “discardable” email addresses with no-hassle. Basically you add a “+tag” to your username. So for example, if your email address is firstname.lastname@example.org, you can add a “+” then any word you want. This gives you a few options when handing out your email address to online forms.
You can use it to help organize your mail. e.g. for all clothing catalogs, you could submit your mail as email@example.com. Your email will still go to your firstname.lastname@example.org mailbox, but you can create filter rules to color or sort your mail based on the “To” address.
Alternatively, you can use it to track down who’s selling your info. Let’s say when you sign up to acme.com, you give your email address as email@example.com. Now whenever you get an email from somewhere, you’ll know where you got it from and when you gave them your email.
It’s also incredibly useful for the developers among us who just need test accounts and don’t want to setup a whole other email. We can easily create firstname.lastname@example.org, email@example.com, firstname.lastname@example.org and use or not-use them arbitrarily.
Additional articles on plus addressing: