SMTP AUTH is not working for a specific mailbox in Exchange Online

Question

SMTP AUTH is not working for a specific mailbox in Exchange Online

Johanson David 20

Hi,

I’m having an issue with SMTP authentication in Exchange Online.

I have a Microsoft 365 mailbox that needs to use SMTP AUTH to send emails from an application. However, the application cannot authenticate and fails when trying to send email.

I checked the mailbox settings in Microsoft 365, but I’m not sure whether SMTP AUTH is disabled for this specific user or at the organization level.

Could someone please guide me on how to:

Check whether SMTP AUTH is enabled for the mailbox

Enable SMTP AUTH for this specific user if it is disabled

Check the setting using Exchange Online PowerShell

I’m a regular user and don’t have full Microsoft 365 admin permissions, so I’d also like to know if an administrator is required to make these changes.

Thank you.

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Answer 1

Dear @Johanson David,

Based on your description, your SMTP AUTH is not working.

Firstly, if you are not Admin, you may need to reach out to administrator for assistance.

Here are recommendations can refer to:

Using the Microsoft 365 Admin Center:

Logging into the Admin Center with an admin account, you can select a specific user and manually enable Authenticated SMTP.

In left menu pane, select Users > Active users > click to the user you want to enable/disable SMTP Authenticated.

User's image

Or you can using Exchange Online PowerShell: (For managing a whole company or troubleshooting a weird error)

To determine whether SMTP AUTH is enabled for a specific mailbox in Exchange Online, an Exchange administrator can connect to Exchange Online PowerShell and run:

Get-CASMailbox ******@domain.com | FL SmtpClientAuthenticationDisabled

Result interpretation:

False = SMTP AUTH is enabled for the mailbox.
True = SMTP AUTH is disabled for the mailbox.

If SMTP AUTH is disabled and needs to be enabled for the user, run:

Set-CASMailbox ******@domain.com -SmtpClientAuthenticationDisabled $false

It's also important to verify the organization-wide SMTP AUTH setting:

Get-TransportConfig | FL SmtpClientAuthenticationDisabled

If the result is True, SMTP AUTH is disabled at the tenant level and an administrator will need to review the configuration.

Since you mentioned that you don't have Microsoft 365 admin permissions, you'll need an Exchange Online administrator to run these commands and make any required changes.

For detailed steps, you can see this Microsoft article: Enable or disable SMTP AUTH in Exchange Online | Microsoft Learn

I hope information above meet your expectations, please feel free to reach out if you have any other questions.

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