Office 365 SMTP authentication failing, even with correct account information

@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

Hey everyone,

For anyone facing the failing authentication issue, I can suggest one thing to try that did solve the problem for me. Granted, there are many possible sources of the problem, so this suggestion won't necessarily fix the issue of course.

In your Microsoft 365 Admin Center under the User tab, you have the ability to allow/disallow Email Apps. Head over to https://admin.microsoft.com/AdminPortal/Home#/users and click on the user that is facing the issues. In the "Email" tab of the modal that opened you'll be able to manage the Email Apps. Select Authenticated SMTP and click save.

In our specific case that fixed the issue.

I hope that helped :)

Cheers

Hey everyone,

For anyone facing the failing authentication issue, I can suggest one thing to try that did solve the problem for me. Granted, there are many possible sources of the problem, so this suggestion won't necessarily fix the issue of course.

In your Microsoft 365 Admin Center under the User tab, you have the ability to allow/disallow Email Apps. Head over to https://admin.microsoft.com/AdminPortal/Home#/users and click on the user that is facing the issues. In the "Email" tab of the modal that opened you'll be able to manage the Email Apps. Select Authenticated SMTP and click save.

In our specific case that fixed the issue.
I hope that helped :)

Cheers

This saved the day for me! Excellent. Can’t thank you enough.

Can @Anna please respond since she is working at microsoft... ?!

We are lots of people with the same issue... Jesus christ, can't be hard to get a real answer..

Hello Adam,

Given this situation, I consider you may login Outlook Web App with impacted account to see if emails can be sent.

If Outlook Web App works well, then check firewall settings, anti-virus or related apps on your server and network, make sure all Office 365 related traffics are allowed: Office 365 URLs and IP address ranges, for some SMTP relay issues are caused by network settings.

You may also refer to this article for troubleshooting: Fix issues with SMTP client submission.

Besides, is there any organization-wide changes made recently? If convenient, use a different Office 365 account to see how it goes.

Best Regards,

Anna

Hello Anna,

I'm having the exact same issue currently.

I have an older account (from January 2020, which is working perfect).

I just got a new account & domain today, and for that one I get exactly the same error as Adam.

I checked with the hosting provider, and no blocks at their end - so this is very strange.

How should I go about it?