Using MailRoute for Forwarding Instead of Exchange Online / Microsoft 365 Forwarding

Note: Forwarding is included in Enterprise and Compliance plans. It is not available for Basics or Legacy plans.

Overview

Forwarding email to external addresses via Microsoft 365 (Exchange Online) can lead to SPF and DMARC failures, especially when emails are forwarded from freemail providers like Gmail or Yahoo. These failures result from Microsoft’s inconsistent application of SRS (Sender Rewriting Scheme) — which is used to preserve SPF alignment during forwarding.

To solve this, you can delegate forwarding to MailRoute, which always performs SRS, even for freemail senders. This ensures high deliverability and standards compliance.

Why Not Use Microsoft 365 Forwarding?

Microsoft 365 applies SRS only in limited cases:

• Messages from “trusted” senders are sometimes rewritten with SRS.

• Messages from freemail domains or other “risky” sources are often not rewritten.

• Microsoft routes these through high-risk outbound pools, where SPF alignment is lost.

This inconsistency leads to:

• SPF failures (message appears to come from the original sender, not the forwarding domain)

• DMARC rejections (especially at Gmail, Yahoo, etc.)

• Bounced emails or delivery to spam/junk

Why Use MailRoute Instead?

MailRoute offers:

• Consistent use of SRS for every forwarded message

• Ability to filter and rewrite emails before forwarding

• Clean delivery to both internal and external recipients

• Simple configuration with or without Office 365 sync

This makes MailRoute a reliable forwarder for scenarios involving external recipients or compliance-sensitive domains.

Setup Instructions

Step 1:  - Prerequesite - Configure MailRoute for Outbound Relay

In order to use this method, you must be using the MailRoute Outbound Relay service.  If you haven't already set that up, you can find info on how to that right here

Step 2: Change Your Domain Type in Microsoft 365

In the Microsoft 365 Exchange Admin Center (EAC):

1. Go to Mail Flow > Accepted Domains

2. Find your domain (e.g., domain.com)

3. Change the type from Authoritative to Internal Relay

Why this matters:

This tells Microsoft 365 to deliver mail locally when it can, but to forward messages to another server (like MailRoute) when it doesn’t find a matching recipient internally.

Step 2: Ensure the Forwarding Address Does Not Exist in Microsoft 365

For the address you want MailRoute to handle (e.g., sales@domain.com):

• Do not create a mailbox, group, distribution list, or contact with that address in Microsoft 365.

• If one exists, delete it.

Why this matters:

If the address exists in Microsoft 365, Exchange will try to deliver it locally — bypassing MailRoute entirely. We want Exchange to treat it as unrecognized, so it forwards to MailRoute.

Step 3: Add the Forwarding Address in MailRoute

1. Sign in at https://admin.mailroute.net

2. Navigate to your Domain admin page

3. Navigate to Users > Email Accounts

4. Click Add

5. In the Email Address (localpart) field, enter the part before @domain.com (e.g., just "sales", for example )

6. Leave the password settings alone — they are not needed for this type of user

7. After creating the address, open its settings and:

   • Enable Forwarding

   • Enter one or more addresses to forward to (e.g., alice@domain.com, bob@gmail.com)

   • Disable “Keep a local copy” 

Note: MailRoute will automatically apply SRS for all outbound forwards to external recipients.

Step 4: If Using MailRoute’s Office 365 Sync, Exclude These Addresses

If you’re using MailRoute’s Office 365 Sync feature:

1. Navigate to your Domain admin page

2. Go to the Office 365 Sync settings page

3. Locate the Exclude Records section (under the Automatic Synchronization settings)

4. Add any forwarding-only addresses (like sales@domain.com) to the exclusion list

This prevents the sync job from:

• Trying to match or overwrite forwarding-only entries

• Deleting the forwarding entry if it doesn’t exist in Microsoft 365

Summary: