Enabling Loopback Detection
The Internet Mail Service allows configurations where SMTP connections are made to itself. There are cases where this is appropriate, such as when a user sends a message to another user on the same server using an SMTP proxy. However, this can also allow loopbacks and inefficient configurations. You can configure the Internet Mail Service so that it will not initiate SMTP connections if the destination host's IP address matches its own. Instead, it creates an NDR for the message.
- Open Regedit.exe or Regedt32.exe.
- Open the following registry keys:
- If you are using Regedit.exe, choose Edit, and then choose New DWORD Value. If you are using Regedt32.exe, choose Edit, and then choose Add Value.
- If you are using Regedit.exe, type DisableLoopbackConnection; under Value data, type 1. If you are using Regedt32.exe, type DisableLoopbackConnection; under Data Type, choose REG_DWORD.
- If you are using Regedt32.exe, under Data, type 1.