Routing Office 365 via Transport Rule for Email Forwarding

Modified on Sun, 16 Feb at 3:04 AM

Problem

Alumni accounts include both users who have mailboxes in the M365 tenant and those who simply need mail forwarded elsewhere. Over time some users with mailboxes will need to be converted to mail forwarding only.

Solution

In Microsoft 365 you can have mail pass through without being stored in a mailbox by using a combination of:

A Group such as a Distribution List
A Mail Flow Rule
A Connector

Prerequisite

The Duocircle Email Forwarding services have been created and configured to accept mail for your domains.

M365 Setup

Here's an example of how this can be accomplished using the M365 UI. Many of these steps can be automated if desired using Powershell.

1. In the M365 Exchange admin center, create a Group such as a Distribution list.

2. For Alumni which have no mail file in M365, they can be added to M365 as a simple Mail Contact with an email address at the same domain used by the tenant.

3. Add all the Alumni with both on-site mailboxes and relay-only requirements into the group you created.

4. In the M365 Exchange Admin Center, create a connector to send mail to DuoCircle's Email Forwarding system:

a. Click 'Add a Connector'

b. In the Connector creation workflow choose:

Connection From: Office 365

Connection To: Your Organization's Email Server

Use of Connector: Only when I have a transport rule set up that redirects messages to this connector

Routing: <Choose one or more from this list for redundancy>

mx1.mailhop.org
mx1.mailhop.us
mx1.mailhop.co
mx1.mailhop.co.uk

5. In the M365 Exchange Admin Center, create a Mail Flow Rule

For the rule conditions, you should specify both the name of the group you created and the connector you created.

6. Note that not all M365 configuration changes go into effect immediately. It could take up to 30 minutes for a new rule to take effect and Connectors can take even longer. We recommend some patience when testing changes to M365 mail flow routing, don't get discouraged if your early tests do not work as expected.