Disclaimer: I don't work for the BPOS or the Office 365 team. For the purposes of this article, I'm just another user/early adopter of cool Microsoft tech. I use Exchange online for my home mail with just a couple mailboxes. I am not tech support (and have no special access to tech support), I'm not an Exchange ninja or DNS guru, and if this doesn't help you, I'm sorry -- it represents the sum total of my knowledge on the subject!

Office 365 is fantastic, and when it goes RTW I'm sure everyone is going to want it. For those of us using BPOS this is an anxiously awaited upgrade. However, if you're using BPOS now and think you're ready to make the switch to the Office 365 Beta, be forewarned: this is not for the faint of heart! According to tech support, its not even recommended!

Keep in mind that Beta software is not intended to be used in production, and BPOS migration has been called out as a feature not implemented in the Beta. With those warnings out of the way, if you're like me and couldn't wait a second longer to upgrade, please heed my advice to avoid days of downtime and pain! Once you've signed up for the Beta, but before you've added your own domain, there are 3 steps you must follow in order to minimize problems during your migration...

Step 1 - Delete your domain from BPOS

Literally, you'll have to remove all e-mail addresses at your vanity domain (you don't have to delete the accounts -- just the @yoursite.com addresses), delete all distribution lists with your vanity domain in the address, then remove the domain from BPOS.
All of this suggests a Step 0 -- you'll likely want to temporarily move your mail and point your MX to another server/service provider. Also, its probably a good idea to copy all of your user's mail either to that temporary server, or into an offline .pst for back-up. There's no easy mailbox migration from BPOS in the beta.

Step 2- Call Forefront tech support and have your domain removed from Forefront too!

Forefront protects mail going into your domain, then routes it to the appropriate Exchange server. If a domain has been previously associated with BPOS, this route must be cleaned out. The only way for this to happen reliably is for tech support to schedule a script to run that will do this -- it can take up to 24 hours, during which time your domain will be provisioned to neither BPOS nor Office365... which is why I recommend a Step 0!

This document gave a US Toll Free support number for Forefront as: 1-866-291-7726

Step 3 - Add your domain to Office365

Create your users and their mailboxes in Office 365. Note that they'll start out with a "yourdomain.onmicrosoft.com" e-mail address and username. You can change this once your domain is added.

Now follow the steps on the Office365 Portal Admin section to add your domain. You'll first have to add a CNAME in your NS to prove you own the domain, then you'll have to turn over your NS to Office365. It won't allow you to just re-point your MX -- you've got to give Office365 complete control over your domain. This ensures that Outlook/ActiveSync can be automatically configured on your devices, and allows you to use Sharepoint on your domain. Don't worry -- Office365 includes a DNS control panel where you can add your own custom entries.

Again, this process can take awhile. Once the MX is changed over, you may experience a briefing (1-2 hour) period where mail bounces back with a "too many hops" error. Inspect the hoplist to make sure none of the servers say Forefront -- which would indicate that Step 2 hasn't been completed. If all of the hops are just Exchange servers, be patient: it will clean itself up shortly. (The site says up to 72 hours, but in practice it seems to be much quicker.)

If at any time you want to double check your settings and proper propogation, use the Domain Troubleshooter in the Office365 and Who.Is DNS Query (or a similar tool on the web.)

When All Else Fails

Hit the forums! There's an active team there watching and responding, and you'll likely find a thread that already solves your problem. If you have to do any troubleshooting, you'll be using PowerShell. Here's how to connect PowerShell to Office 365 -- make sure you run it as Administrator on your box.

Again, this is Beta software -- migrations are a manual process right now, but once you get it done, its well worth it! Office365 rocks!