After all on-premises mailboxes are migrated to %BRAND_OFFICE_365_SHORT%, you can configure an Autodiscover DNS record for ...

After all on-premises mailboxes are migrated to %BRAND_OFFICE_365_SHORT%, you can configure an Autodiscover DNS record for %BRAND_OFFICE_365_SHORT% to enable users to easily connect to their new %BRAND_OFFICE_365_SHORT% mailboxes with %BRAND_OUTLOOK_SHORT% and mobile clients. This new Autodiscover DNS record must use the same namespace that you're using for your %BRAND_OFFICE_365_SHORT% organization. For example, if your %BRAND_OFFICE_365_SHORT% namespace is contoso.com, the Autodiscover DNS record you need to create is autodiscover.contoso.com.