Sendmail "ok" signal?

[Gaz]

Hey. I looked at the Sendmail help and did not find a property where i
can get an "ok" signal when the email is finally sent. I need something
like that to show a "Processing, please stand by" screen when the
server is sending an email, and when the email is out, another screen
appears with an "Email sent" message.

Do you know an alternative to the "ok" from the sendmail to do this?