You probably know that you can create multiple emails in Gmail by adding the plus sign or dots in the name of the user, but below we will see something more interesting.
By creating one account Gmail, Google has two email addresses for you. One uses the regular domain and is @ gmail.com while the second address is under another domain: @ googlemail.com.
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.