Create security groups. Because the email migration service can't detect whether on-premises Active Directory groups are ...

Create security groups. Because the email migration service can't detect whether on-premises Active Directory groups are security groups, it can't provision any migrated groups as security groups in %BRAND_OFFICE_365_SHORT%. Any mail-enabled groups in your on-premises directory will be migrated as distribution groups. If you want to move these groups as security groups instead of distribution groups, you must first provision an empty mail-enabled security group for each of these groups in %BRAND_OFFICE_365_SHORT% before starting the cutover migration. To create a mail-enabled security group, see Create, edit, or delete a security group in the %BRAND_OFFICE_365_SHORT% admin center.