SSO between Two Forest for Exchange Email Access

Hi Friends,

I would like to provide email services to our partner company(different forest). Please share your views/suggestion to provide SSO to Partner company users for email access (OWA, Exchange Activesync, Outlook Anywhere, Exchange online, for all Email related services)

Overview :

Own Company (Forest 1): Exchange 2010  

Partner Company(Forest 2) : Exchange 2003

Requirement : Need to migrate Partner company users mailbox to own company exchange 2010 server. Migrated email box need to be access by partner company users using their own AD authentication (SSO).

Is this requiremet can be met by ADFS 2.0? or any other possiblities.

Please help me by sharing your recommendations.

Regards, Mohan - Technology