Login to Gmail.
On the left, click Gmail, then Contacts in the dropdown menu.
In the bottom right, click the red circle to add a new contact (not very intuitive, I know).
Enter the name of your contact. For an email address like email@example.com, simply enter yourwebsite.com for the name.
Click where it says Add an email.
Enter the email, such as firstname.lastname@example.org.
To go back, click on the left arrow or anywhere on the dark gray around the box. Again, this wasn’t very intuitive for me either.
Be sure to whitelist your email as well so it doesn’t go into Spam.