Microsoft recent change to Office365 related to SMTP Authentication(Enable or disable SMTP AUTH | Microsoft Docs. The change will disable SMTP Auth at the tenant level, as a result Power365 will not be able to send out cutover notification email using the PowerShell user.
Power365 does not use the PowerShell User as the default sender for these notification emails, it will only be used if the Admin Account does not have mailbox enabled and unable to send the notifications via Graph API (MS Requirement to use Graph API). When this happens, as a result Power365 will then rely on PowerShell user as a backup. Now due to this recent Microsoft changes, if the tenant has disabled SMTP AUTH, PowerShell user will fail to send the email as well.
Also, it looks like this setting will be disabled for all new tenants, we are not sure if this affects existing tenant yet, but it is likely MS will start rolling out this changes to existing ones.
Since this is a tenant setting at the client end, Quest has no control over this configuration. The only work around is to enable SMTP AUTH at the mailbox level if it is disabled for the entire tenant. Tenant admin should run the below PowerShell command.
Set-CASMailbox -Identity BinaryTreePowerShellUser.John.Doe -SmtpClientAuthenticationDisabled $false