Invalid email when registering

Hi.  I read through this thread https://help.forumotion.com/t106305-registration-email-error-sorry-but-this-e-mail-address-is-invalid?highlight=invalid+email
for any tips, but could not fix the issue.

I have a person trying to join my forum, using an email address from their company website.  This person is the owner of the company and the company website. The website has not been in operation but a few months. It keeps getting rejected as invalid.  The email address is valid as I have exchanged emails with this person via the email address.

Any ideas on how to correct this?

I have tried to set up an account using another email address, and changing it manually on the users profile, but still get the same message.

Hello Hammer,

Could give me the url of your forum please ?

Is he the only user having some problems to connect on your forum?

Thanks