Linux – Postfix Mail

Hi

I am using Mandrake Linux 9.2. We use postfix as our mail server. Our ISP provides the Mail Firewall (Mail Marshal) It seems that we are not receiving mails from the one domain client. They are receiving our mails, but when they reply or send a new mail, we don?t receive it. We are receiving mails from all other mail accounts.

I do receive the mails if they send it to my external mail account. I have looked @ the mail reports on the Mail Server, but I cannot not find any of those mails. Our ISP confirmed that the mails has gone through to our Mail Server. What now?

Please advice

Thank you

Morn?