Conditional Access for external SMTP authentication

[Brian Hoyt]

We only have one use for external services sending via Office 365 in an authenticated method. I was hoping to use conditional access to restrict only one account to be able to authenticate into SMTP. I want to block all other users from being allowed to authenticate into SMTP. Is this possible?

[#2 · Accepted solution]

You can disable SMTP AUTH globally for your organization by using Exchange Online PowerShell. And then enable it per mailbox in the Microsoft 365 admin center or using Exchange Online PowerShell.
https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client...