Hybrid Setup Using SmarterMail and Microsoft (Office) 365

Occasionally, a business may need to run a hybrid environment consisting of SmarterMail and Microsoft 365. This is generally due to some users having existing Microsoft 365 accounts while others will be using solely SmarterMail. However, it can also be useful during a migration from Microsoft 365 to SmarterMail to ensure email messages are not lost or orphaned.

This is accomplished through Split Domain Routing (SDR). SDR allows users with email addresses in the same domain to receive emails at two different email service providers. It involves configuring DNS records and email forwarding rules to manage how emails are delivered to different servers.

To set this up in SmarterMail, what you will need to do is to go to the domain settings for that domain and adjust the inbound delivery setting. 

1. Log in as a system administrator, select the domain, and go to its Options tab.
2. Here you will see a card labeled Email.
   
3. On that card, change the Inbound Message Delivery setting.
4. In order to enable Split Domain Routing, choose either "External" option, then fill in the necessary information. The following External options are available:
   • External (use MX record) - Select this option if the mail server is hosted partially or entirely externally. Messages will be delivered based on an MX lookup. Select the option "Deliver locally if user exists" to perform a local delivery instead of external if the user exists locally.
   • External (use host address) - Select this option if the mail server is hosted partially or entirely externally. Messages will be delivered to the specified host address. The host address can either be entered as an IP address or the Fully Qualified Domain Name (FQDN), such as mail.yourdomain.com.  
5. Make sure to enable Deliver locally if user exists to perform a local delivery instead of external if the user exists locally.

Things to Note

If you have Require SMTP Authentication enabled for the domain on its Security card, you will want to add a Bypass SMTP Authentication for that domain in its Security settings.  

1. As a system administrator, go to Settings -> Security and click on the Whitelist tab.
2. Click the New button and fill out the following:
   1. Source = Domain Name
   2. Domain Name = {enter your domain name here}
   3. Description = Some friendly text, like "Split domain whitelist for domain_name" or something similar.
   4. Enable Bypass SMTP Authentication under Security.
   5. Be sure to save the changes.