Workitem with user X, Email sent to user Y

Hi Experts,

We are facing a typical case in our ECC system.

Appreciate your inputs ...

Standard report RSWUWFML2  is being used to send the email notifications to the work item holders.

User X has the workitem in his SAP inbox. But user Y receives the email notifications for this workitem in his mailbox.

Issue is with only one user here. Email in su01 is correctly maintained for both users X,Y. Any suggestions to trace and correct this.

Thanks in advance

~Ali~