Office 365 (Outlook on the Web) - Create a Custom Contact List
The ability to create Groups in Outlook on the Web has been turned off by the network administrator. The solution is to instead create a Contact List. This list will reside in your Contacts only and cannot be shared with or edited by others.
2.) Select the People icon from within the column in the upper left.
3.) In the upper left of the screen, select New contact>New contact list.
4.) Give your contact list a name, type in the email addresses or names of the users you would like to add, create a description if applicable, and then click Create.
5.) It will be saved to Contacts>Your contact lists within People. When your contact list is selected, you will see an option to Send email to this list - OR - within a new message in Outlook, enter the name of your contact list in the To field.