ShellExecute(0, 'open', 'mailto:a...@b.c', '', '', SW_OPEN);

I'm using Delphi 5 here, and I pop a label on the form and set its font
properties to blue / underlined.  I set its cursor property to
crHandPoint.  Then I use the following OnClick event handler for the
label...

procedure TWhatEverForm.emailClick(Sender: TObject);
var
  emailAddress, emailSubject, emailBody, emailStr: string;
begin
  emailAddress := 'mailto:y...@email.address.here';
  emailSubject := '?Subject=' + Application.Title;
  emailBody := '&Body=Write me a note here !';
  emailStr := emailAddress + emailSubject + emailBody;
  ShellExecute(0, Nil, PChar(emailStr), Nil, Nil, SW_SHOWNORMAL);
end {TWhatEverForm.emailClick};