UPDATE - the double sending problem will be fixed on Wed 10/21. Thanks for your patience.
With the last release there are a couple of problems affecting some users. On certain browsers in certain configurations, the Send function in Web Mail is sending two copies. This will be fixed soon. The other new issue is that some users of IE are getting a message "An internal error occurred" after sending a message. The message is sent correctly and only the error message is wrong. This also will be fixed shortly.