PO Communication to suppliers through Email

Hello Everyone,

we have configured workflow mailer for po communication through emails and emails are being generated when we communicate a po using the communicate option in        PO summary > Tools > Communicate.

What our client is expecting that when we approve a PO the email should be generated automatically and the email address should be defaulted form the supplier's contact information. In the PO approval window this option is available but how can we default the email address.

Thanks in advance,

Israr