MX record setting

Hi,

When a mail exchange server, like hotmail.com, receives a mail from ‘originalsenderdomain.com’ with ‘From’ address as ‘fromaddress@fromdomain.com’, does hotmail exchange server look for an ‘MX’ record against ‘originalsenderdomain.com’ or ‘fromdomain.com’ domain?

The reason why the original sender domain is different from fromdomain is because we need to collect bounce records on a different server.

So, is it sufficient if i set an ‘MX’ record for ‘fromdomain.com’?