EDIT 10/4/2007: Since this post has been published, we have updated the Exchange 2007 Autodiscover Service whitepaper to include this information. Please consult the whitepaper for most up-to-date ...
Updated Jul 01, 2019
Version 2.0
Blog Post
Hey Mecsi,
There is going to be a whitepaper coming out very soon that should cover all of your questions, however I don't thing it is going to cover 'Hosted Exchange' or 'Hosted Messaging and Collaboration' (HMC).
That being said, here are some brief answers to your questions:
1. Hosting (multiple emaill domains) is a huge topic that deserves it's own blog. You should start here:
http://www.microsoft.com/technet/serviceproviders/hmc4/cmsu_hep_plan_conc_heprovisioning.mspx
2. Setting external URL for redundancy. Redundancy doesn't come from Exchange in the CAS role, it comes from a NLB appliance or server and you should set the externalurl value to the external NLB address (if you want that farm of CAS server to proxy to other sites). This is no different that E2K3 FE configuration.
3. Multiple AD sites. There are a lot of things you need to decide about this. Do you want to proxy the requests from a central site or do you want to redirect users to CAS servers that are local to the mailbox sites? If you want to proxy, configure your NLB but don't set the external URL. If you want to redirect, set up NLB at each of the sites and configure the externalURL appropriately.
4. Growth. If you follow the above and need to add an additional CAS box, then all you need to do is install the box and then add it to the NLB farm. You'll re-use the cert on each of your CAS servers (remember the privatekeyexportable option?).
5. Adding another email domain (hosting). See answer to 1.
There is going to be a whitepaper coming out very soon that should cover all of your questions, however I don't thing it is going to cover 'Hosted Exchange' or 'Hosted Messaging and Collaboration' (HMC).
That being said, here are some brief answers to your questions:
1. Hosting (multiple emaill domains) is a huge topic that deserves it's own blog. You should start here:
http://www.microsoft.com/technet/serviceproviders/hmc4/cmsu_hep_plan_conc_heprovisioning.mspx
2. Setting external URL for redundancy. Redundancy doesn't come from Exchange in the CAS role, it comes from a NLB appliance or server and you should set the externalurl value to the external NLB address (if you want that farm of CAS server to proxy to other sites). This is no different that E2K3 FE configuration.
3. Multiple AD sites. There are a lot of things you need to decide about this. Do you want to proxy the requests from a central site or do you want to redirect users to CAS servers that are local to the mailbox sites? If you want to proxy, configure your NLB but don't set the external URL. If you want to redirect, set up NLB at each of the sites and configure the externalURL appropriately.
4. Growth. If you follow the above and need to add an additional CAS box, then all you need to do is install the box and then add it to the NLB farm. You'll re-use the cert on each of your CAS servers (remember the privatekeyexportable option?).
5. Adding another email domain (hosting). See answer to 1.