In the event log you see the problem while testing the connection .
An error occurred while opening mailbox .
Solution:
The best way is to play with access credentails and use enter the user name
and password while configuring the incoming and outgoing access credentails. The user must be able to open the mail boxes in exchange.
please go through from this post .
“The user must be able to open the mail boxes in exchange.”
How much is realistic?
Really it is useful post and that i want to read these techniques as well as I will be having a go and thanks for sharing such sort of techniques please ensure that it stays sharing.