SMTP Traffic from Outside of Forest Generates NDR

Inbound Internet mail is returned to the sender with a non-delivery receipt (NDR) with the following error message: The NDR contains at least two attachments, one of which is a .txt file that contains the following error message:
The NDR may have an attachment with a name similar to "ATT00086.dat". It can be opened with Notepad and the content will be: No related limitations are configured on the SMTP connector or the SMTP Virtual Server.

An incorrect or missing domain entry in Internet Message Formats can cause this problem. By default, the entry is named "default," and has a domain value of "*" (an asterisk), which allows all domains to send messages to this server. For example, changing the domain to a company domain causes mail sent from an address outside Active Directory to be returned with the errors listed in the "Symptoms" section. Removing the entry has the same effect.

To resolve this issue, re-create (if necessary), and set an Internet Message Format entry to Domain that is equal to "*".

To Re-Create an Entry

1. Start Exchange System Manager Microsoft Management Console (MMC).
2. Expand Organization Name (Exchange), and then expand Global Settings.
3. Right-click Internet Mail Formats, click New, and then click Domain.
4. Type the name of your choice in the Name box. Enter an asterisk
   *
   in the SMTP domain box, and then click OK.

If you only need to modify an existing domain entry, follow these steps:

1. Start Exchange System Manager MMC.
2. Expand Organization Name (Exchange), and then expand Global Settings.
3. Expand Internet Mail Formats; double-click the Domain entry that you wish to modify.
4. Type the name of your choice in the Name box. Enter an asterisk
   *
   in the SMTP domain box, and then click OK.

You can find Internet Message Format under Global Settings in the Microsoft Exchange System Manager snap-in.