List of emails forwarded to a user

Hello All, 

I apologize if this issue have been solved before. i am trying to know the List of emails forwarded to a particular user in MS Exchange Server 2010 SP3. 

I used this command;

Get-mailbox -ResultSize unlimited | select DisplayName,ForwardingAddress | where {$_.ForwardingAddress -ne $Null}

But it listed all the mail forwarding in the entire exchange mailbox. I just need to obtain all the email addresses that are forwarded to a certain user. lets say; i want to know to know all the email addresses of users that is being forwarded to "Alan John".

Please help. I will appreciate this.

many thanks