I'm deciding whether to accept a new registration using an email that already exists in the database but using a different username or to refuse it.
There are times when I forget username and/or password for a website. I then try to re-register using a different username/same email I used but often get refused by some web apps.
What is your opinion on this?
Edit: Forget this other important question...
When trying to see if username already exists in the database during registration, should I do case sensitive comparison? Should different case use create different usernames?
What about passwords? Should they be case sensitive?
Thanks!