What is the exact error you get?

The mail server returns the mail as not able to be delivered and tells me it is a permanent error. The email address is correct. I have been given another company email address to send to and that has the same end result. I am not blocked by them and all my other emails are being sent to their destinations. What else can I say?

You can post the error verbatim. as a delivery failure notification contains reasons and error codes. Is contains more that "not able to be delivered" and "a permanent error"

Also what email provider are you using? My guess is it is a hosted domain. If that is the case, who is your host and what is the domain name?