issue in incoming e mails for some users

recently i faced an issue with one of my customers which was really strange and i decided to blog about it

the issue was some users are not able to receive e mails from certain domains, when we check message tracking, no trace for the message, we enabled pipeline tracing and also no trace for the message, if the sender sends an e mail to the user and another few users in his organization the message is received for all users except the problematic user and the odd thing is that the user is not in the header of the message which means something is filtering the user before it even arrives at exchange server, we checked customer network devices and even we replaced some appliances with no luck, then we found that what is common between the problematic users are all having black berry accounts

and that's when we found that the messages were going to black berry instead of exchange server