[DoctorOhh]

Originally Posted by Manichean

Your username needs to be your full GMail address including the domain, so use either user@gmail.com or user@googlemail.com depending on what your address is.

That's a myth or to be more exact, I never add the @gmail.com when signing into gmail or when sending books via calibre. If my email address was peter.rabbit@gmail.com all I ever enter in the username field to log into my account (or send via calibre) is peter.rabbit, add my password and I'm logged in.

I believe you have to enter the full email address when listing it with Amazon as a authorized email address.

Update: full username@gmail.com may be required in some locales.