By creation one account Gmail, Google has you covered two διευθύνσεις ηλεκτρονικού ταχυδρομείου. Η μία uses το κανονικό domain και είναι η @gmail.com ενώ η δεύτερη address is under another domain: @ googlemail.com.
This means that if your Gmail email address is firstname.lastname@example.org, all messages e-mails sent to email@example.com you will also have them in the inbox of firstname.lastname@example.org.
Two in the "price" of one.
How can you use the second address?
You can take advantage of these two domains for less spam in your email inbox.
For example, @ googlemail.com can only give you your close contacts. The email you use as domain gmail.com can be used publicly (put it on your blog, for example).
You can then set a filter in Google's email service that will redirect all messages from @ googlemail.com to a special folder. So you will never lose important email from your close friends.