Try to use the website content, providing you mail. Let's say you are signed out and you available your login. Most often, it is the main component of the email address. Add to it the sign "dog" and the domain. For example, if the login issue, and the site then e-mailЧтобы to know I was right there in conjectures, try to send any email to this e-mail.
Some sites let you select multiple domains to login. If you can't remember it, you can try out all the options. As a rule, not more than four. Follow the same rules – send an email to yourself and choose the one that will reach the recipient.
If you leave someone your email address, then contact them and ask them to remind your e-mail. You can also poll their friends on the subject of whether they remember your email. Often loved ones know your address and can help. It is also recommended to colleagues at work, who may send you important information.
If you have access to email but you do not remember their own addresses, just look in the "Sent" folder. Usually in the 'from:' field will contain your e-mail, also you can contact the technical support site, which in 99% of cases will help to resolve the situation.