When you submit an email through
telnet and choose not to authenticate, the server assumes that you are
anonymous (aka the well-known
NT AUTHORITY\Anonymous logon or
Send-MailMessage submits an email, it will ALWAYS try to authenticate the session. If a set of credentials is not specified, it will assume that the current users network credentials is to be used, and authenticates as the service account running the PowerShell script.
The service account is neither anonymous, an Exchange User nor an Exchange Organization Administrator and will not be permitted to submit the email.
The work around this, you'll need a
$anonUsername = "anonymous"
$anonPassword = ConvertTo-SecureString -String "anonymous" -AsPlainText -Force
$anonCredentials = New-Object System.Management.Automation.PSCredential($anonUsername,$anonPassword)
Send-MailMessage -to "Big Boss <firstname.lastname@example.org>" -from "Me <email@example.com>" -subject "It's working! EOM" -credential $anonCredentials
Now your script is sending mails anonymously as well :-)
Another (and more secure) option is to give the service account in question the required permissions on a receive connector:
$RC = Get-ReceiveConnector "ConnectorNameGoesHere"
$RC | Add-ADPermission -User "DOMAIN\ServiceAcc01" -ExtendedRights ms-Exch-SMTP-Submit,ms-Exch-SMTP-Accept-Authoritative-Domain-Sender
If you need to transfer files that will potentially be removed by content filtering or the likes you can also allow it to bypass anti-spam mechanisms:
$RC | Add-ADPermission -User "DOMAIN\ServiceAcc01" -ExtendedRights ms-Exch-Bypass-Anti-Spam
If you want it to send emails to recipients outside your own Exchange Organization you'll need to allow that as well:
$RC | Add-ADPermission -User "DOMAIN\ServiceAcc01" -ExtendedRights ms-Exch-SMTP-Accept-Any-Recipient