You can try by including library d2kwutil.pll (to use this you need d2kwutil.dll, that doesn't work on windows2000), wich is included in forms.
Then your code to send an email (without atachment) will be like this:
declare
destinatarios varchar2(100):='null@null.null';
var1 varchar2(100)='test subject';
var2 varchar2(100)='test';
BEGIN
WIN_API_SHELL.WINEXEC('C:\iexplore.exe '||' /MAILURL:MAILTO:'||destinatarios||'?cc='||' '||'&subject='||var1||'&body='||var2,WIN_API.SW_SHOWNORMAL,TRUE);
END;
Hope this helps