Setting up a rule for a Distribution Group to external senders

Step 1 – Open Rules

Step 2 – Click on New Rule

Step 3 - Select "Apply rule to messages I receive" and click Next

Step 4 - Select "sent to people or public group". In the lower pane, click "people or public group", and in the Rule Address dialog, select your distribution list. Click To to add it to the rule, then OK, to close the dialog, then click Next.

Step 5 - Select "have server reply using a specific a specific message". In the lower pane, click "a specific message", and when you see a new message open, add a subject and body of your message to match your response. Click "Save and Close" to close the message, then click Next.

Step 6 - Select "except with specific words in the sender's address". In the lower pane, click "specific words", and in the Search Text dialog, enter each of the email domains of your organization ("company.com", "subsidiary.com", etc). When you have all domains listed, click OK, then Next.

Step 7 - In the next page of the Wizard, you can change the name, enable the rule. When done, click Finish to close the Wizard. But don’t run on existing messages or it will send replies to all messages of that type already in the inbox.

Step 8 - Once you have the rule completed, save it by clicking OK (or Apply, then OK, if you prefer)