Questions about migrating to Exchange Online...

I am trying to migrate from an on-premise Exchange 2010 server for a small office. I don't want any AD integration, this is strictly a cut-over. I plan to migrate the data over a period of about a week or two. Looking up the documentation, I had a couple of questions that I have not been able to get a clear answer for.

1) If I migrate all of the data for a given mailbox one day, can I migrate only the changes that have occurred if I run it again just before the cut-over?
2) If I setup my Exchange Online account with the domain, will other people who use Exchange Online send to the Exchange Online account or will they use external DNS for the MX lookup? I had this issue when I was migrating a client to Rack Space and I needed to tell them to force external lookups for the domain.

Can someone point me in the right direction for this? Thanks!
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Vasil Michev (MVP)Commented:
1) The cutover process will periodically do incremental syncs after the initial one (every 24h)
2) If the recipient can be found in EO, the mail will be delivered there. If the recipient is not found within EO, you will either get an NDR (if the domain is set to Authoritative) or get redirected based on the MX value (if the domain is set to Internal relay). Remember that you will have to deal with the "reverse" situation as well - on the on-prem server the mailbox will still exist and internal messages will be delivered there, regardless of where the MX points at. While the incremental sync will take care of these messages (with delay up to 24h), once you finish the migration it's recommended to convert the on-prem mailboxes to mail users.

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medium_gradeAuthor Commented:
For users in EO in the same organization, yes I understand. But what about EO users in different organizations?
Vasil Michev (MVP)Commented:
They will send where the MX points at.
medium_gradeAuthor Commented:
Are you sure? When migrating to Rack Space, I had a problem in which, when I created a mailbox for a user in their environment, other Rack Space customers mail would go straight to the new Rack Space mailbox even though the external MX records pointed elsewhere.
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