Below are the URLs that are used by Read&Write for Windows that you may need to whitelist on your firewall:-
Note: Whitelisting the top level domain *.texthelp.com will allow access for all .texthelp.com URLs listed below.
Note: These URLs are required for Picture Dictionary
Note: These URLs are for providers that are used for signing into Read&Write for Mac and Windows. URLs for providers that are not used can be ignored