Why do I get the error message "Sender address rejected: need fully-qualified address "
This is happening because your SmtpMail.SmtpServer is rejecting addresses.
To resolve this make sure
- all email addresses specified at MailMessage.To, MailMessage.Cc, MailMessage.Bcc and MailMessage.From are valid email addresses
- you have permissions to relay through the server.
- MailMessage.From has permissions to relay through the server