[ubuntu-uk] Replacing Evolution with Thunderbird in right-click "Send to" menu

I've set Thunderbird as the preferred mail reader, but if I right-click
on a document or file and choose "Send to" the only option available to
me is Evolution.. I don't use Evolution because I find the Thunderbird
calendar more useful. How can I remove Evolution from the "Send to"
options and replace it with Thunderbird?

thanks