Not sure what the problem could be. One thing is certain though. Its not the BB at fault. It is the mail server. You may work around this by setting up a forwarding rule. Forward the emails from the problem email address to the Blackberry email address.
Edit the Blackberry email address and add the problem email address in the reply to field, add your name in the your name field. Save and resend service books. You are doing so as when you reply to an email on your bb for this email address it will appear to the recipient as if you have replied from the original (problem) email address.
Let me know how it goes!