I don’t know way but in the last 2 days I could not use GMail as default program for mailto addresses, looking around I found this post in the Google support.
The solution below was exactly what I needed.
I report the solution if any of you may need it
1. Enable javascript handling in Chrome. You may be able to do this through the options menu, but I did it manually.
"protocol_handler": { "excluded_schemes": { "afp": true, "data": true, "disk": true, "disks": true, "file": true, "hcp": true, "javascript": true, "mailto": false, "ms-help": true,
2. Launch Chrome
3. Open GMail and login
4. In the address bar type or copy and paste
javascript:window.navigator.registerProtocolHandler(“mailto”,”https://mail.google.com/mail/?extsrc=mailto&url=%s”,”GMail”) or if you have multi account
javascript:window.navigator.registerProtocolHandler(“mailto”,”https://mail.google.com/mail/u/0/?extsrc=mailto&url=%s”,”GMail”)
and press Enter or hit Go.
5. You’re done.
6. To cleanup, close Chrome, change the javascript setting back to true in Local State.