1. On the network tab: under "User this local IP adresses to receive mail: "Use all available IP adresses on this server" under "Receive mail from remote servers that have these ip adresses: Add all IPs which must send emails 2. On the Authentication tab: check Transport Layer Security (TLS) check Exchange Server authentication leave all other unchecked 3.On the Permission Groups check Anonymous Users leave all other unchecked Have you set the powershell command from my previous post?: Get-ReceiveConnector “relay” | Add-ADPermission -User “NT AUTHORITY\ANONYMOUS LOGON” -ExtendedRights “ms-Exch-SMTP-Accept-Any-Recipient” "relay" should be replaced by the name of your connector.