Login Failed?

[Delta555]

Tried the search function, didn't find anything on this issue.

I'm sure it's trivial but I added a e-mail address to Thunderbird and it worked, however when I restarted the program it asked for a password for which I don't remember putting one on aside from the email acct password and when I enter it, I am shown the above error.

I'm sure i'm simply missing something but some help would be much appreciated, thanks in advance.