No. The username is part of the e-mail address, which is username@domain.dom.
Not exactly. An email address can be compared to your home address, only the email address is online. An email can be compared to a letter. Like a letter is sent to your physical address, an email is sent to your email address.
The same reason your house address is unique. To address mail to a specific destination.
You cannot track anyone from the mail. The email firstly cannot be changed after creation. You have to remain with the same address as before.
No, "e-mail" should not be capitalized; it is not a proper noun.
Same reason you need an address to receive mail. It's how myspace contacts you if they need to.
A regular address book holds names, addresses, phone numbers, etc. An E-mail address book contains the same information, except it also has E-mail addresses and is the computer version of a regular address book. Many people's E-mail address book is also called a Contacts list-- it depends on what E-mail program you use.
The same way you would with any other computer, I guess.
The opening and closing salutations for an email should use exactly the same criteria as other mail. It depends on the formality of the mail and to whom it is addressed.
No. Everyone has to have a unique address email within a domain, so that the mail gets delivered to the proper place.
You can only have one account per e-mail
No, two people can't use the same e-mail address on facebook, however you can associate one e-mail address with different pages on facebook, such as business, organizations, and personal pages.