Acoount BLOCKED, "Reason UNKNOWN"

Hi good evening, i have this trouble.. one of my clients are so mad becasue his email account ( gerardo_hernandez@cocinte.com) have the outgoing blocked around 2-3 days ago... can u help me to unblockit? it's very important to us, because they are a vip client of our bussines, the saturday i've already sent an email, but i still get no reply... have a nice day