re :I've attempted to retrieve my username several times.

In a mail account, the 'User Name' is usually the full email address, but on some occasions it may be only the part before the @ sign.

Perhaps you mean you are wanting to reset a password to a mail account because you forgot your old password.

Do you usually input the password each time or did Thunderbird remember it? Because if TB usually remembers it then the old password could be in Thunderbird.

senario example: If you have a website hosted by someone and you forgot the password to access that account email address, then they would send an email to the email address which you have registered with the webhosting company as an alternative contact email address and it would not be connected to your website email address. After all, how could you see any email sent to an email account which you cannot logon to see. So, it may be your email address as provided by ISP.

Can you explain your situation?

retrieve 'username' for what? Obviously you are not talking about the username for a mail account in Thunderbird.

Perhaps it is a username for some webpage/forum/chat site. If they sent an email, you would need to know which email address would be receiving it.

If you have a pop mail account and the email got caught by the server filter, then it could be in the webmail account spam folder. Pop mail accounts can only download if email is in server Inbox.

Have you logged on to your webmail account to see whether you are receiving those emails, but they were auto moved to server Spam fodler?