you can configure the logging settings in universal email to log failure or success in the email log database.
to access the logging settings, click on the icon of the envelope with the green checkbox and red cirlcle on it.
the logging options will record in the database whether the email was successfully sent to the SMTP server for each address or not.
If it is being sent to the smtp server, you will need to contact the host to determine why the smtp server is not relaying the email to that user.