Few Supervisor is not getting the Email for approval to approve the leave but in their Self Service

When any users are raising leave approval request to their supervisor, they are getting the FYI notification that you leave has been sent for approval to you super visor.From: Workflow Test Mailer [mailto:wftest@ABC COMP.com.bh]
Sent: Tuesday, April 23, 2013 10:09 AM
To: S**** B****
Subject: FYI: Leave Of Absence has been forwarded to R** R A*** E*****

From SYSADMIN
To S****** F********
Sent 23-APR-2013 10:09:13
ID 8####
Last Approver: S****** F********
User Name: S********
Comments:

Next Approver: R** R A*** E*****
User Name: R********

This notification is for information only.

But the Supervisor is not getting the Email for approval to approve the leave but in their Self Service Notification they are getting the approval frame work page.. And this is happening to only few particular Supervisors.Other Supervisor are getting the Email Approval page and they are approving it through Email.