Quick help for filtering – Email notifications *were* working until new server

Built a new site for client and used Formidable forms for a simple follow-up form. Tested and everything worked great including the email notifications until the client’s dedicated email provider upgraded their exchange server. I BCC’ed multiple other addresses with tests, they all receive fine, so I know it is some sort of filtering on their end.

They are asking me what the SMTP server that is delivering via wordpress. If anyone has any specific tips or ideas that can solve this quickly, please advise. I am not very confident they will find the answer based on questions they are asking. If I have to send to a different email and redirect those with a separate rule, I’ll do that if needed, but it seems like this would be a quick fix.

Thanks for your help!!