After setting up Co-Existence Manager's Mail, Dirsync and Free/Busy Connector, the Free/Busy [FB] request from a Domino user via notes client to a migrated user to Exchange doesn’t work.
FB requests from Outlook to Notes works fine.
SMTP name space on both sides is domain.com
SMTP forwarding SMTP namespace from domino to exchange exch.domain.com
The issue was was that the foreign SMTP domain was in the format "exchange.domain.com". Changing it to "*exchange.domain.com" enabled free/busy & email-coexistence work at the same time.
Note the * adjacent to the subdomain and not *.subdomain.domain.com