[exim] Serach / Replace.

I need a filter which triggers when a message is sent from a certain
user to a non-local user. (That's the easy part), and I would like to
replace every occurance of

http://portal-1/

with

https://portal.company.com/

But, I am not sure what the best way to do this is?

The mails are generated from Microsoft Sharepoint Portal Server, so they
are RTF/HTML/something, but a straight search/replace should still work?