Recently, the GMX email service has dropped thier support for PLAIN authentication. This means that the CR1000/CR800/CR3000 will no longer work with their email service.
It is recommended that those who where using this email system (GMail and Yahoo as well) should switch over to the new EMailRelay() service. EmailRelay() is a service and system that Campbell Scientific owns and maintains that will allow customers with CR1000/CR800/CR3000 dataloggers to use this service for their messaging needs.
Details concerning EmailRelay() and how to use it can be found at https://s.campbellsci.com/documents/us/technical-papers/emailrelay-function.pdf
The CR6 and CR300 dataloggers continue to work with GMX, Yahoo, and GMail for email and messaging. Users should use STARTTLS authentication instead of PLAIN on these dataloggers (see the help for the UserName option used by the EmailSend() instruction in the CRBasic Editor for details).