I can turn off IMAP on an individual user basis (POP3 not turned on) But is there a way of doing it for authenticated SMTP short of deploying a VPN? Exchange Online has the command: Because legacy authentication protocols don’t support interactive sign-in, which is required for additional security challenges like multi-factor authentication and device authentication. Users would get the popup constantly and it was causing a lot frustration for both our users as well as our support team. Due to the way basic authentication works the end-user experience is not pretty and will not be pretty. In this case, you will have to update or configure them in a special way to switch to Kerberos. The following table explains client behavior while working against Exchange, SharePoint and Skype for Business tenants in Office 365. Legacy authentication is unsafe because you can’t enforce multi-factor authentication on them – that’s why enabling MFA for your users isn’t effective if you don’t block legacy protocols.
Disable legacy authentication exchange 2016 If you want password synchronization or Pass Through Authentication, stick to Azure AD Connect.
