Enable or disable authenticated client SMTP submission (SMTP AUTH) in Exchange Online

[daniele]

1) Connect to Exchange online via Powershell
(Instructions for Windows - check on Internet for updated and complete instructions)

INSTALL Exchange online management tools

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Install-Module -Name ExchangeOnlineManagement

LOAD Exchange online management module
Import-Module ExchangeOnlineManagement

CONNECT AND AUTHENTICATE to Exchange online management module
Connect-ExchangeOnline -UserPrincipalName <UPN> [-UseRPSSession] [-ExchangeEnvironmentName <Value>] [-ShowBanner:$false] [-DelegatedOrganization <String>] [-PSSessionOption $ProxyOptions]

2) Check if SMTP AUTH is enabled for the whole tenant

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Get-TransportConfig | Format-List SmtpClientAuthenticationDisabled

3) Enable (or disable) SMTP AUTH for the whole tenant

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Set-TransportConfig -SmtpClientAuthenticationDisabled $true

(or $false)

3) Enable (or disable) SMTP AUTH for a specific mailbox

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Set-CASMailbox -Identity <MailboxIdentity> -SmtpClientAuthenticationDisabled <$true | $false | $null>