I have a similar problem, but I'm providing an invalid recipient address instead. I want an exception to be thrown, but none is. After attempting to send my message, I later got an email message from the SMTP server saying the mail was undeliverable (as expected). It seems that the SMTP server accepts the bad email and closes the connection with your program, so your program thinks everything is ok. Then, the SMTP server actually tries to deliver the mail. Does anyone know of a workaround so that your program knows whether or not the message was successfully delivered? Thanks