This is a possible solution:
declare MailAdr as type System.Net.Mail.MailAddress.
declare expMess as type System.Exception.
try
set MailAdr to new System.Net.Mail.MailAddress(textBox2::Text)
catch expMess
invoke type System.Windows.MessageBox::Show(expMess::Message, "MailAddress invalid")
end-try.
Werner Lanter