I have a bug in my site. There is a page where the user put his email as the first step for the registration process. So an email is sent to this direction to complete the registration process. But now appears this error message in the page:
Mailbox name not allowed. The server response was: sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)
I ask the hoster but it told me that there is a error in the code. Probably there is a simple solution, but I will pay US$ 50,00 for an inmediate correction in the code and the page working well again.