Onsite SMTP Relay to Office 365 – 535 5.7.3 Authentication unsuccessful

This is due to SMTP client Auth flag not allowing this type of connection.

$UserCredential = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell-liveid?DelegatedOrg=<[email protected]> -Credential $UserCredential -Authentication Basic -AllowRedirection
Import-PSSession $Session -DisableNameChecking

Set-TransportConfig -SmtpClientAuthenticationDisabled $false