Office 365 SMTP authentication failing, even with correct account information

Have you tried the solution I've posted?

Having the same problem. Has anyone found a resolution to this latest SMTP authentication problem? MS Office tells me to pay my web host to fix. Web host tells me MS 365 should fix it. Anyone from Microsoft listening?

I was struggling with that too. Finally I found a solution which requires to change properties in Azure Active Directory (Properties > Manage Security Defaults). You have to turn off "Enable Security defaults" like at the linked screenshot from the documentation.

The starting point to find that solution was **Microsoft 365 Admin Center > Settings > Org settings > Services > Modern authentication.**The link to the above mentioned documentation is provided in description of Modern authentication.

Now I'm able to send emails by SMTP protocol with using an app password from MFA enabled account.

I have checked everything outlined here and i still have the issue

-Modern auth is off

-SmtpClientAuthenticationDisabled $false

-User SMTP is ticked

-Security defaults is off

The worst part is i went over all this then it worked last week, then a week later with no tenant changes it is not working

As a last ditch i toggled all the settings encase they were displaying incorrectly or some such and it still won't work.

I have also created a brand new user and applied the relevant settings and it also does not work.

Side note when enabling 2 factor App passwords cannot be created even tho the option is on, and there are no policy's preventing it as polices aren't available in the license.

In the documentaton it says "If your authentication policy disables basic authentication for SMTP, clients cannot use the SMTP AUTH protocol even if you enable the settings outlined in this article. For more information, see Disable Basic authentication in Exchange Online."

Since Microsoft Security Defaults disables basic authentication does this solution still works?

Kind Regards,

@all i think this ist the solution:

I had the same Problems, old offic365 accounts work, new accounts did not work. After searching for 5 hours i get a solution:

In the old accounts SmtpClientAuthenticationDisabled is false by default on online Exchange, in the new accounts it is True by default.

I had to set it to false by exchange online powershell and also hat do go to e-mail-apps and set the hook to authenticated smtp

after that it worked. Here you can read what is to do by exchange powershell:

https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission

Steps in Powershell:

$UserCredential = Get-Credential

$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection

Import-PSSession $Session -DisableNameChecking

Take a look if it is True: Get-TransportConfig  (if there is True set to false)

Set-TransportConfig -SmtpClientAuthenticationDisabled $false

Take a look again if it works: Get-TransportConfig

Remove-PSSession $Session

In Admin Center --> acitve Users --> click the user --> email-apps --> click the hook --> authenticated smtp

With this combination it worked for me. Hope this can help you all