I'm often surprised by the amount of Gmail users that don't realise just how powerful their email address can be. For example, did you know that if you have an email address such as: firstname.lastname@example.org
You will also receive all emails to the following addresses...
email@example.com firstname.lastname@example.org email@example.com firstname.lastname@example.org
...and so on.
But more usefully, you can also add additional words to your email address using the + symbol. This is especially useful when using online forms on websites that you rarely visit but need to enter your email address to access. Everyone knows that when you sign up to websites with your email address you automatically get added to a mailing list and therefore run the risk of a massive amount of spam emails in your inbox, but sometimes it's necessary to see the content that you want to see.
So Gmail has the answer. Simply add the name of the website in front of your email address like this:
email@example.com firstname.lastname@example.org email@example.com
That way you know exactly who is sending you spam emails, selling your email address and adding you to unwanted mailing lists. You can even set up a filter in Gmail to put all emails addressed to a certain address into it's own folder (or if necessary, auto delete).
It's a very useful feature. Unfortunately it doesn't always work though - some websites filter out the + symbol and won't allow you to sign up using an address with it in. But in my experience, the majority will allow.