When you sign up for an Office 365 subscription you may be asked to choose a domain (depends on the subscription). The name you choose here forms the onmicrosoft.com
domain that is initially provisioned in the tenant (you can add others, see later)
For example, when I first signed up I chose my own company name – Konnexion. The resulting domain was thus konnexion.onmicrosoft.com. It’s a simple matter to add additional domains later and in my case I added konnexion.com as that’s where I want my email to be delivered and originate from.
That initial tenant domain name choice is crucial – you cannot change it later. It becomes your root SharePoint site collection – in my case https://konnexion.sharepoint.com. It also forms the OneDrive URL for each user – https://konnexion-my.sharepoint.com.
If you decide later that the name you initially chose is unsuitable, or you face a company reorg etc, there is currently no way to rename this. You have two options at this stage ..
- Live with it, it’s purely cosmetic, though your CEO may not agree.
- Create a second tenant and migrate all data from the old to new tenant.
That second option hides a world of pain, especially if you have been using the initial tenant for some time, as all data in Exchange, SharePoint, Planner, Teams, Yammer etc may need to be migrated. I say may because you will almost certainly decide to abandon some of this data.
Third party migration products exist for some of these workloads – namely Exchange & SharePoint but for others there is no easy way to export/import the data from old to new. To further complicate such matters it’s entirely probable that you will be managing two tenants while migration takes place, with users existing in both. It’s all about the planning.
Microsoft have been promising for some time now that they will provide a way to rename a tenant. That has not appeared as yet and there’s a lengthy Uservoice discussion around this topic that stretches back to February 2016.
So for now, choose that domain name very carefully !