Inbound email IP reputation checking with EOP

Hi,

Does anyone know exactly if/how Microsoft performs IP reputation checking for inbound messaged to O365?

I have an issue where our email is being forwarded though another SMTP server before it reaches office365 so any IP reputation checking is negated. Out antispam performance is underwhelming so I'd like to know to what degree it would perform better with email going directly to EOP.

thanks,

Tony.