Microsoft 365 Split Delivery

If you use Microsoft 365 for your primary mailboxes but want ImprovMX to handle catch-all addresses or specific aliases, you can configure split delivery. Microsoft 365 will handle known users while forwarding unrecognized recipients to ImprovMX.

Prerequisites

• Full admin access to your Microsoft 365 account
• Your domain's MX records pointing to Microsoft 365 with higher priority than ImprovMX
• Recommended: Disable Strict MX Verification if applicable, to avoid alerts about lower-priority MX records

Step 1: Configure Domain as Internal Relay

First, change your domain type to allow Microsoft 365 to relay emails for unrecognized recipients.

1. Open the Exchange Admin Center
2. Navigate to Mail flow > Accepted domains
3. Select your domain and click Edit
4. Change the domain type from Authoritative to Internal Relay
5. Click Save

Note: Setting your domain as Internal Relay tells Microsoft 365 to forward emails for unknown recipients to another mail server instead of rejecting them.

Step 2: Create an Outbound Connector

Next, create a connector to route unrecognized emails to ImprovMX.

1. In the Exchange Admin Center, go to Mail flow > Connectors
2. Click Add a connector
3. Configure the connector:
   • Connection from: Office 365
   • Connection to: Partner organization
4. Click Next and enter a name (e.g., ImprovMX Connector)
5. Under Use of connector, select Only when email messages are sent to these domains
6. Add your domain (e.g., yourdomain.com)
7. Under Routing, select Route email through these smart hosts and add:
   • mx1.improvmx.com
   • mx2.improvmx.com
8. Under Security restrictions, enable Always use Transport Layer Security (TLS)
9. Click Next, review your settings, and click Save

Step 3: Configure ImprovMX Aliases

In your ImprovMX dashboard, create the aliases you want to forward. For example:

• info@yourdomain.com → your-personal@gmail.com
• * (catch-all) → catchall@gmail.com

Step 4: Test the Configuration

After saving your settings:

1. Send a test email from an external account to a Microsoft 365 user — it should be delivered to their mailbox
2. Send a test email to an ImprovMX alias — it should be forwarded to your configured destination

Important: Ensure all your ImprovMX aliases are configured before testing. Microsoft 365 will relay unrecognized emails to ImprovMX, and ImprovMX will bounce them if no matching alias exists.

SPF Configuration

When using both services, combine the SPF records into a single TXT record:

v=spf1 include:spf.protection.outlook.com include:spf.improvmx.com ~all

See our guide on combining SPF records for more details.