Basic Authentication Deprecation in Exchange Online – September 2022 Update

PeterForster There will not be any changes for SMTP auth for those customers that are actively using that protocol, so basic auth for SMTP protocol will not be disabled. As Nino Bilic mentioned earlier, the option to opt-out was there for those customers not actively using it, and the basic auth might have been disabled, they could then opt-out, but again, since the  Set-TransportConfig -SmtpClientAuthenticationDisabled $true/$False or Set-CASMailbox -Identity sean@contoso.com -SmtpClientAuthenticationDisabled $True/$false would Disable/Enable basic auth for SMTP auth, then you don't need to run the opt-out diagnostic, you just use those PowerShell cmdlets in case you need to enabled basic auth for SMTP, again as I mentioned earlier as well, the best practice is to disabled it at the transport level and enabled it for those mailboxes that need it:

Set-TransportConfig -SmtpClientAuthenticationDisabled $true      #diabled it at transport level
Set-CASMailbox -Identity sean@contoso.com -SmtpClientAuthenticationDisabled $false      #enabled it for the mailbox that needs it.