First of all, "go offline" in Sales for Outlook (SFO) does not work when the users recide in a trusted NT4 domain. We never got to test "go online" for obvious reasons. This might be due to v1.2 using SQL Replication, which in v3.0 has been replaced by the good, old BCP tool. Note that v3.0 still uses MSDE as the offline database and not SQL Express. Both SQL Server 2000 and 2005 are supported by MSCRM 3.0 as the master database.Then the famous "E-mail Router": setting up routing of incoming e-mails as shown in the implementation guide works, sort of. Install a new Exchange Server in the AD domain and use either a CRM subdomain or forwarding of non-CRM e-mails to the original Exchange Server. Beware of the small print, however! Only e-mails to mailboxes registered in the native AD domain of MSCRM will be processed by the router. Thus, mails to a user will not be routed, even when a reply to a MSCRM e-mail, as they are in the NT4 domain. The only AD mailboxes we had were for queues (email@example.com, etc), and routing of incoming e-mails to these queues works like a breeze.
We are currently deploying MSCRM 3.0 in a simmilar scenario, this time with five customer divisions, each with its own AD domain that are not within a single, common AD forest. Each domain (customer division) has its own Exchange server. I will post our experiences on the limitations with this infrastructure later on.
Note that an Exchange 'organization' cannot span AD forests, and that MSCRM is limited to one Exchange 'organization'. This restricts MSCRM with full Exchange e-mail functionality to a single AD forest.