You want to tell the friend the e-mail address that he could write you, but find out that you cannot make it because you do not know own address. Quite seldom, but it happens. There are several ways of definition of own address e-mail.
Check the guess, having sent any message to the address defined thus. If it returns to you, so you defined it correctly.
2. Some servers offer, in addition to the login and the password, also to select one of several domains at an input. What you got used to select from them, on it and your mailbox is located.
3. Some users got used to work with the mailbox only through the special program, but not via the web interface. If the program is configured in such a way that the input is carried out automatically, such users quite often forget not only the password, but also the login and the domain. It is possible to learn the last two parameters, having entered settings of such program (how exactly - depends on what program is used). They are in the section devoted to accounts.
4. On some servers during registration it is possible to receive if desired the user name (which is contacting the addresses), not matching the login. In this case, it is possible to learn the address, having come into the Sent folder and having opened any of messages. Your address, or, at least, a user name (depending on the server), most likely, will appear in the graph "From Whom".
5. If in this column are not shown neither the address entirely, nor a user name but only a nickname (on some servers happens and so), it is necessary to define the e-mail address in the indirect way. Send to the friend whose mailbox address you know, the message, and then ask it to tell you from what address it came.
Itself can also register one more account on other server, this time having carefully written the address given you. Send the message from an old box which address you want to learn to it. When it comes to a new box, you learn its address at once.