Ronald,

I found a much simpler way of achieving this. Although
it's not activated by a button I've inserted a hyperlink
and by adding "SendTo:" in front of the e-mail address
the user can now open a Outlook new message by clicking
on the hyperlink. Applying protection to the sheet
prevents any changes being made to the address.

The alternative was a sledgehammer to crack a nut
scenario.

Many thanks,
Ray.