[Exim] Simple Address Rewrite : foobar@mydom.dom --> 12345@p…

I am trying to forward a email location to a pager which has a numercial
address like 12345@??? but the to header should contain the
"12345@???" for it to accepted for paging so could anybody tell me
how to go about writing a Address rewrite for just "To:" field and not
to evevlop...

Rewrite should be

To : foobar@??? ----> To : 12345@???

Any help is greatly apperciated...

TIA
Nagendra
VU2CLN