Plan a custom domain for your Microsoft 365 deployment

  • 4 minutes

There are several factors an organization must consider when planning to add custom domains to Microsoft 365. These factors can differ with the Microsoft 365 subscription it selects.

The following table sets out the planning factors that must be taken into consideration.

Factor Considerations
Multiple domains An organization should plan to add the main domain that it currently uses (for example, adatum.com for Adatum Corporation). It should also add any other domain that it uses for email messages within the organization. This scenario is common when the overall company is a business group. It's also common when an organization undergoes a merger process and some employees still have alternative email addresses.
Subdomains An organization may want to register subdomains. Microsoft 365 Business Premium and Enterprise plans enable subdomains to be added under the root domain. For example, within the adatum.com root domain for Adatum Corporation, the company added a subdomain specific to the Sales department titled sales.adatum.com.
Domain numbers An organization can register up to 900 domains with Microsoft 365.
Domain adding order Root domains must be added before subdomains. So in the previous example, the adatum.com root domain must be registered before the sales.adatum.com subdomain is added.
DNS record hosting An organization’s DNS servers or an external hosting provider can host DNS records.
Access to the DNS console An organization should check with its DNS hosting provider about the level of access that it has to the DNS console. To configure its Microsoft 365 services, an organization must have access to add the A, CNAME, TXT, MX, and SRV records. If the DNS hosting provider doesn't provide that level of access, the organization may have to send a request to the DNS hosting provider to change DNS records needed for its Microsoft 365 deployment.
Not registering DNS It's rare that an organization wouldn't want to register a DNS domain with Microsoft 365. However, it does happen occasionally. For example, an organization may want a separate email and directory service for its Microsoft 365 users. One possible scenario is a university that wants to host its faculty members in the on-premises environment and have the students in Microsoft 365 with a different domain name.
Not changing all records An organization may not want to change all the DNS records to point to Microsoft 365. An upcoming unit in this module identifies how to handle the verification process when you don't change all the DNS records.