Windows 7 Set default "mailto" handler when registry protocol branches empty?

I have problems to set an eMail client (e.g. Thunderbird) on my 64bit Win 7 system for handling all "mailto" links. It is often recommended to go to

Control Panel --> Set Default programs

or

Control Panel ---> "Associate a file type or protocol with a program"

and assign the (new) email client here.
But this doesn't work here since the underlying protocol entries are missing.

Have a look at the attached snapshot; As you can see: There is NO "mailto" protocol entry here (...which I could change)!

I tracked down the problem to the Registry and found empty Registy branches for

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\mailto

and

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Classes\mailto

I think the are accidentially deleted in the past.
So what I need is a zero-assumption initial Registry re-fill for "mailto".

How can I re-create Registry key branches to any email client or the protocol itself.

I think when this is done I can easily re-assign the mailto protocol to other software.

Peter