How Outlook 365 (Mail Client) works with your email account servers: Adding an email account to the Outlook 365 app means that your email server folders sync to the app and you benefit from all the great features that the client app gives you (for email, contacts and calendar) compared to using webmail. If you have a Microsoft account (outlook/live or hotmail) you also benefit from having your contact (People) and calendar servers sync as they use ‘Microsoft Exchange’