Out of Office for External Users not working.

There is two thinks that can be configured in order to allow OOF messages in Exchange:

Under Get-RemoteDomain

and Get-mailbox | fl *ExternalOofOptions*

For the first we should enable following:

Get-RemoteDomain Default | Set-RemoteDomain -AutoReplyEnabled $true -AutoForwardEnabled $true -AllowedOOFType External

For the Mailbox

Set-Mailbox usermailbox -ExternalOofOptions external

Event with all this in place sometimes the OOF messages are still not delivered. We have to use MessagerTracking in order to see why.

If we have something in front of the Exchange it is very likely that this device can block messages with ReturnPath <>  black.

This is often a case when you have Smarhost which is forwarding the messages. in this case we can see in Message tracking .

RecipientStatus         : {[{LRT=27.06.2017 07:25:27};{LED=554 5.7.1 <>: Sender address rejected: Access denied};{FQDN=host.fqdn.com};{IP=196.168.0.1}]}

554 5.7.1 meens -“relay access denied” .

You have to execute the tracking with | fl to get the hole information.

This bahavior for Out Of Office messages is by design since exchange 2013 and it is event in the standart RFC2298

https://www.ietf.org/rfc/rfc2298.txt

The envelope sender address (i.e., SMTP MAIL FROM) of the MDN MUST be null (<>), specifying that no Delivery Status Notification messages or other messages indicating successful or unsuccessful delivery are to be sent in response to an MDN.