Our client's external OoO is not working or more likely being rejected. When I did Exchange message tracking on the automated reply, it fails with an error message: "550 5.5.0. Sender Domain is empty". The customer is using a Smart host pointing to our Fortimail appliance for a spam filtering, but I can't find the message being logged on our end anywhere (Fortimail). I've also disabled any Content filtering on customer's Exchange(for testing only) to no avail.
I know a workaround would be to use DNS (MX) records to route the mail out instead, but they'd get smashed with SPAM obviously..
Was somebody else experiencing this please?
Thanks a lot