Configuring Microsoft Office 365 for MailRoute takes a few steps. But it's important that they be done in order. This article makes it look like it's a lot, but we've tried to be very complete and show you each and every step along the way. It's not really that difficult.

The first step is to configure MailRoute for your inbound email flow. If you're a new customer, we may have already done this for you. If you are changing from another service or an in-house server, you may need to do this yourself (or ask us to help!)

Then we will set up Transports to handle inbound and outbound email flow, and a rule that prevents anyone from bypassing MailRoute and sending email directly to Microsoft.

Microsoft talks about some of this stuff in their article Managing mail flow using a third-party cloud service with Exchange Online

We're going to do these things in order:

Configure MailRoute with your Inbound Email Server
Change your MX record to mail.mailroute.net
Add your SPF, DKIM, DMARC, and ADSP records to your DNS server
Configure an Inbound Transport in Exchange online to allow Office 365 to identify that your mail is coming from a trusted partner who is doing email filtering for you
Configure an Outbound Transport to tell Office 365 to send your outbound mail out through MailRoute
Configure Advanced Filtering for Connectors in Exchange Online to improve your filtering and reduce false-positives on the Microsoft side

Step 1. (Which we may have already done for you!) - Configure Inbound Email Server in MailRoute Control Panel

Locate your Office 365 mailserver hostname in the Microsoft 365 Admin Center: https://admin.microsoft.com/#/Domains
- Select your domain, and then click DNS records. You'll find your inbound Office 365 mailserver listed in the MX record under Microsoft Exchange. It will look something like this: example-com02c.mail.protection.outlook.com
- Visit the MailRoute Admin center at https://admin.mailroute.net, and select Domains at the top, and then click on your domain in the list
- Then Choose Inbound Servers from the menu at the left, and then click the Add button:
- Enter in the Office 365 Mailserver, and set the priority to 10, and click Save:
- Set your Server Type by clicking the edit button, and then setting the Type to Office 365 and then clicking Save.

Note: MailRoute will automatically recognize that you are relaying email out from Microsoft, so there is no need to set up an Outbound server in the MailRoute Control Panel for your outbound mail.

Step 2. Change your MX Record to mail.mailroute.net

This will start the flow of email through MailRoute!

We have articles on how to do this for many common DNS providers at https://support.mailroute.net/hc/en-us/sections/205311968-Changing-MX-Records

Step 3. Add SPF, DKIM, DMARC, and ADSP records

To properly protect your outbound mail, add your SPF, DKIM, DMARC, and ADSP records while you're in there changing your MX record.

We have a primer on what all these are for, if you're interested here: https://support.mailroute.net/hc/en-us/articles/360061128614-Email-Authentication-An-Explanation-and-Exploration

We have a Knowledge Base articles for each of these:

Step 4. Configure Inbound Transport

Microsoft uses an inbound Transport to identify email that comes in via MailRoute to prevent false-positives from their own email filtering.

Visit https://admin.exchange.microsoft.com/#/connectors to manage your connectors.
Click Add a connector
Choose Partner organization and click Next:
Give your connector a name like MailRoute Inbound, be sure Turn it on is selected, and then click Next:
In Authenticating sent email, choose the option By verifying that the sender domain matches one of the following domains, enter *.mailroute.net and click the + (plus) icon to add this sender domain. After it's added, click Next:
In Security restrictions, choose the checkboxes Reject email messages if they aren't sent over TLS and And require that the subject name on the certificate that the partner uses to authenticate with Office 365 matches this domain name and enter *.mailroute.net into the text field, and then click Next:
In Review connector, verify that everything looks good, and then click Create connector:

Step 5. Configure Outbound Transport

Microsoft uses an outbound Transport to identify route outbound email out through MailRoute, so that we can improve our filtering accuracy and give your domain even more protection.

If you're not still there, visit https://admin.exchange.microsoft.com/#/connectors to manage your connectors.
Click Add a connector
In the New connector window, choose Connection from Office 365 and Connection to Partner organization, and click Next:
Give your connector a name like MailRoute Outbound, be sure Turn it on is selected, and then click Next:
In Use of connector, choose Only when email messages are sent to these domains. Then enter * in the text field and click the + (plus) icon to add this sender domain:
After it's added, click Next:
On the Routing window, choose Route email through these smart hosts, enter outbound.mailroute.net into the text field and click the + (plus) icon to add this SmartHost:
Now that it's been added, click Next:
Under Security restrictions, choose Always use Transport Layer Security..., and then Issued by a trusted certificate authority (CA) and Add the subject name or subject alternative name (SAN) matches the domain name and enter *.mailroute.net into the text field, and click Next:
in Validation email, enter an email address that is outside your own domain for testing. You can use the same one as we do here, if you would like (test@mailroute.net). Enter the email address into the text field, and then click + (the plus symbol) to add the address:
Then click Validate and wait a bit for the test to run.
Once it's done, and it shows that it's successful, click Next:
In Review connector, make sure it all looks good, and hit Create connector, and then press Next to finish this up!

Step 6. Configure Advanced Filtering for Connectors in Exchange Online

This will reduce false-positives on Microsoft's side and improve filtering effectiveness. It also prevents people from bypassing MailRoute and sending email directly to you without filtering.

Microsoft has an article explaining how it all works at https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/use-connectors-to-configure-mail-flow/enhanced-filtering-for-connectors#what-happens-when-you-enable-enhanced-filtering-for-connectors

Jump right to the configuration page at https://security.microsoft.com/skiplisting
Click on your MailRoute Inbound connector
Choose Skip these IP addresses..., enter 199.89.0.0/21 into the text area, and then choose Apply to the entire organization, and click Save: