Mail Responses For Approvals Are Not Working

My user needs to have the ability to approve expenses and purchase order by email. He is receiving the email approval notification and when he click the "Approval" link,  it generates an new email to sent email to ofa-wf-prod@company.com with the following information:

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- To:  ofa-wf-prod
-subject: Action Required: "the issue"

Action: 'Approve'

If forwarding this document to another person, please enter their user-id
below
Forward To: ''

Note
Note: ''

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And the document is not move from que to approval. Looks like the approval is not able to identify the next approver?

Note: user is using MAC and using Mac OS X 10.6.8 platform