Improve internal (same domain) email deliverability for Office 365

To ensure that emails delivered from CM.com to your own DRB Office 365 installation are not incorrectly labelled as spam, it is a good idea to add the IP Addresses (from which your emails will be delivered) to the Allowed List in the Connection Filtering Policy within the Office 365 Exchange Admin Centre (EAC).

The main benefit of whitelisting is that your email will automatically bypass unnecessary spam filters (as you have sent the emails).

To add CM.com IP addresses to the Office 365 "IP Allow List":

1. Sign into Office 365 and click "Admin", then under "Admin Centers", click "Exchange"

2. Under the "Protection" list, choose "Connection Filter"

3. Click the "Edit" button which looks like a pencil

4. Choose "Connection Filtering" on the left side menu

5. Click the plus "+" symbol and add an IP range from the list below and click "OK"

6. Repeat step 5 until the IP ranges below have been entered

7. Check the "Enable Safe List" checkbox

8. Finally, click "Save"

Instructions for the new Exchange Admin Center:

1. Sign into Office 365 and go to the "Security Center" https://security.microsoft.com/homepage 

2. In the left side menu under “Email and collaboration” go to “Policies and rules”

3. Click the “Threat policies” option

4. Under “Policies” click “Anti-spam”

5. Click “Connection filter policy (Default)” so the options appear on the right side and then click the “Edit connection filter policy” link

6. Add our IP ranges from below to the “Always allow messages from the following IP addresses or address range” section

7. Check the “Turn on safe list” checkbox

8. Finally, click “Save”

The IPs that needs to be added are: 
188.94.184.36;
188.94.185.36;
188.94.184.37;
188.94.185.37;

In case the above will not work, we suggest to contact with office 365 support team through the Microsoft ticketing system.
How to: https://support.microsoft.com/en-us/topic/contact-microsoft-office-support-fd6bb40e-75b7-6f43-d6f9-c13d10850e77