Unable to send the email
When using the “Test” button and the “From” email address is set to the "Contact's Owner” the system is going to use the default user. If you receive the following error it is because the default User has no email address saved.
Navigate to the Default Users record and save an email address. Once an email address is saved in the email field you can send your test email. Note: You do have the option of selecting a different Default User.