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Use Exchange Online PowerShell to enable or disable SMTP AUTH on multiple mailboxes This example disables SMTP AUTH for mailbox Set-CASMailbox -Identity -SmtpClientAuthenticationDisabled $true This example enables SMTP AUTH for mailbox Set-CASMailbox -Identity -SmtpClientAuthenticationDisabled $false The mailbox setting takes precedence over the organization setting. You use the values $true (disabled) or $false (enabled) to override the organization setting. The value $null indicates the setting for the mailbox is controlled by the global setting on the organization. Use the following syntax: Set-CASMailbox -Identity -SmtpClientAuthenticationDisabled Use Exchange Online PowerShell to enable or disable SMTP AUTH on specific mailboxes When you're finished, click Save changes. Verify the Authenticated SMTP setting: unchecked = disabled, checked = enabled. In the Email apps section, click Manage email apps.
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Select the user, and in the flyout that appears, click Mail. Open the Microsoft 365 admin center and go to Users > Active users. Use the Microsoft 365 admin center to enable or disable SMTP AUTH on specific mailboxes
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The per-mailbox setting to enable (or disable) SMTP AUTH is available in the Microsoft 365 admin center or Exchange Online PowerShell. To verify that you've globally disabled SMTP AUTH in your organization, run the following command and verify that the value of the SmtpClientAuthenticationDisabled property is True: Get-TransportConfig | Format-List SmtpClientAuthenticationDisabled Note: To enable SMTP AUTH if it's already disabled, use the value $false. To disable SMTP AUTH globally in your organization, run the following command: Set-TransportConfig -SmtpClientAuthenticationDisabled $true You can only disable (or enable) SMTP AUTH globally for your organization by using Exchange Online PowerShell. For more information, see Disable Basic authentication in Exchange Online. 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 What are security defaults?. If you've enabled security defaults in your organization, SMTP AUTH is already disabled in Exchange Online. Note that these settings only apply to mailboxes that are hosted in Exchange Online (Office 365 or Microsoft 365). A per-mailbox setting that overrides the tenant-wide setting.An organization-wide setting to disable (or enable) SMTP AUTH.There are two settings that can help you do this: Therefore, we highly recommend that you disable SMTP AUTH in your Exchange Online organization, and enable it only for the accounts (that is, mailboxes) that still require it. Virtually all modern email clients that connect to Exchange Online mailboxes in Office 365 or Microsoft 365 (for example, Outlook, Outlook on the web, iOS Mail, Outlook for iOS and Android, etc.) don't use SMTP AUTH to send email messages. SMTP AUTH supports modern authentication (Modern Auth). The SMTP AUTH protocol is used for client SMTP email submission, typically on TCP port 587. For more information, see Authenticate an IMAP, POP or SMTP connection using OAuth. As of February 2020, OAuth authentication is available for POP3, IMAP4, and SMTP AUTH connections to Exchange Online.