1. First of all, we need to understand the composition of the e-mail address: the format of the e-mail address consists of three parts. The first part of the "USER" on behalf of the user mailbox account, for the same mail receiving server, this account must be unique; the second part of the "@" is the separator; the third part of the user mailbox mail receiving server domain name, to mark the where it is located.
2. Understanding the composition of the e-mail address, we can then fill in the e-mail address. The separator "@" will not change, when we know the recipient's mail server domain name, such as QQ mailbox, then "@" is qq.com; and 163 mailbox is 163.com.
3. "@" in front of our e-mail address is the user name, such as user name "123456" QQ mailbox, then the complete e-mail address is "123456@qq.com "; another example, the user name "999" of the 163 mailbox, the complete e-mail address is "999@163.com" visible as long as we know the user name and domain name of the mailbox, you can spelled out the complete e-mail address.