2.71.0 export not working

I just downloaded the newest edition, converted some books and tried to send to my Amazon via gmx. It failed here:

SIZE 69920427
AUTH LOGIN PLAIN
send: AUTH <censored>
reply: '535 Authentication credentials invalid\r\n'
reply: retcode (535); Msg: Authentication credentials invalid

Sending failed...

Traceback (most recent call last):
File "site-packages\calibre\gui2\email.py", line 44, in run
File "site-packages\calibre\gui2\email.py", line 134, in sendmail
File "site-packages\calibre\utils\smtp.py", line 139, in sendmail
File "site-packages\calibre\utils\smtplib.py", line 647, in login
SMTPAuthenticationError: (535, 'Authentication credentials invalid')

Any ideas as to why?