Hello NorfolkGreg
I just tested your calendar.
On the 2. October you have an event where there is a link Elaine Smith.
When I click this link I see an informational message that says :
Send mail to : elainesmith364@btinternet.com
And when I say "yes" to this, it opens my Outlook and starts a mail
In the TO field : elainesmith364@btinternet.com
And in the subject field : 02/10/2018 - 1st Stalham Rainbows
I would say, that this should be the way it should function.
When I do it for the event on 13. October and click on Diane Godron then the
TO field contains : mailto:concert@stalhambaptist.org.uk
And the subject : 13/10/2018 - Gospel Night
So - maybe you should just remove the mailto: