Our company's email is hosted Exchange 2016 (hosted by AppRiver). It's a simple setup: only ~100 mailboxes, single domain, no linkage between Exchange and our corporate file/print/login AD, no public folders, etc.
Our company was just acquired by another company that uses Office 365 (managed by a reseller). The acquirer, although larger than us, is also pretty small: under 200 users.
Now we need to figure out the best path to get our email/calendar/contacts integrated with the acquirer. The desired end-state:
- all mailboxes end up on the acquirer's O365
- emails sent to our "old" email addresses end up in the right user's mailbox
- all emails sent from our company use the acquirer's email addresses, even if they were sent to our old email addresses.
- calendars, mail, and contacts and mail continue to work as before for end-users with relatively little user training or disruption. For example, requiring users to delete and re-add their email accounts in outlook and phones is OK. But users having to re-create all calendar invites and contacts would not be OK. Email being unavailable for a weekend is OK, but not OK if it's a full week.
- we can stop paying AppRiver within a few weeks after migration is complete.
- we don't need to do a phased migration-- it's OK to migrate all mailboxes at once.
The options I've heard so far are:
- Create new mailboxes in the acquirer's O365 account, and then migrate mail and calendar info from one mailbox to the other.
- Migrate mailboxes directly from hosted exchange at AppRiver to O365
- Migrate from AppRiver's hosted exchange product to O365 resold by AppRiver. Then migrate from AppRiver O365 to the acquirer's O365.
What are the pros/cons of each of these options? Will one of them be much easier/better than the others? Is there another option that's better than all of above?