Do I have a unique Instapaper username?

Every Instapaper account needs to be tied to an email address, primarily for things like password recovery. Passwords are not required, but most users do have a password. Any interface prompting the user for credentials must accommodate this -- for example, you cannot assume that an empty password is a user error.

Authentication behavior:

• If an account has a password and an incorrect one is supplied, authentication fails.
• If an account does not have a password, any value works.