KB ID 0001418 Problem This is Part-One of a migration from ‘on-premise’ Microsoft Exchange, to Office 365 (Exchange Online). I’m using my spare ‘test domain’ (.co.uk). And I’m using the 5 user E3 Office 365 subscription that the good folk at Microsoft let me have, as part of my MVP benefits. Note: I’m using Exchange 2016, with a ‘full-hybrid’ migration into Office 365. Step 1: Pre-Requisites DNS: You will need access to the DNS records for your public domain, both to ‘prove’ it is your domain, and to divert mail flow, and client requests to Exchange online, rather than your on premise Exchange. Licenses/Subscription: You need an office 365 subscription, and available licences for all the users you want to migrate. At time of writing the minimum subscription level that includes Exchange Online is E3. (Note that’s not strictly true, you do get Exchange online with E1, but you dont get any office products, so I’ve never seen an E1 licensed migration). You’ll need to have access to Office 365 with a ‘global administrator‘ account. Backups: Not really a pre-requisite, but how are you going to backup your cloud mailboxes? As far as Microsoft is concerned, your online email gets deleted after its retention period, (amount of time after a user deletes it, i.e. up to 100 days). If your business continuity plan, requires you to keep mail ‘x‘ years, then you will need to think about Azure Backup, or a third party backup solution. Existing Exchange: Unless you are going to use a third party migration tool, then your on premise Exchange needs to be at Exchange 2010. So if you’re still at Exchange 2007/2003/2000, then you need to either; 1) Upgrade your on-prem Exchange, 2) Do another on-prem migration before you start, or 3) Purchase a third part migration tool. Note: With Exchange 2007 you can add one Exchange 2010 Exchange server, then migrate. Certificates: You MUST HAVE a certificate on your Exchange that is publicly singed by a third party certificate vendor. There’s no excuse to use self signed certificates these days, (for Exchange). For this exercise I bought a certificate for a year and it cost me less than ten dollars, thats half the price of a one users monthly licence for Office 365? WARNING even with a correctly setup PKI environment with publicly published...