For canceling of sending the e-mail it has to be executed one or the other conditions: you should use Gmail service or Microsoft Outlook program 2007 or 2010, and at the same time to have the Microsoft Exchange Server 2000, Exchange Server 2003 or Exchange Server 2007 account. In all other cases it is not possible to withdraw the sent letter.
The problem of obtaining the password from mail by the login rises before forgetful users quite often. But all modern mailboxes have function of password recovery by the login. Also this function is used by hackers for cracking of accounts.