iPrint Appliance Mail serring fail

Hi All
I want to enable iprint email printing function, and then I create a new mail account from my Exchange 2007 server, and then try to login this user to MS OWA page. Yes this user could login well.
now I login appliance console, enable mail printing function...I typr like below:
Maill Address: ipuser01@sna.com.tw
Account Name:ipuser01
password:P@ssw0rd
re-type password:P@ssw0rd
incoming mail server:192.168.0.251
incoming server type: IMAP/POP(I tested 2 type...all fail)
outgoing mail server:192.168.0.251

But appliance show "changes cannot be saved because of the following errors: Could not authenticate email settings.Reason: Failed to connect to mail server for ipuser01@sna.com.tw"

I indeed believe these user information correct, which log I could check in appliance ?

thanks!!

wyldkao