Is your username your email and What is my username if my email is 12345678.com?

It can be but it usually asks for ur email seperatly but if u want is to be it can. It doesn't need to be though.:-)

No. The username is part of the e-mail address, which is username@domain.dom.

You cant really change an email name, but you can create another one and transfer all conversations and contacts and emails ect. or convert to gmail. gmail is a very good email/chat client. i would...

importance of username in creating email account

The user name is what the person chooses when he or she first creates a new e mail account. This is most typically their first name and surname (e.g.Gordon Brown or they may choose their initial(s)...