Overview


When using the Vitanium Mail Filter (or any third-party cloud email filtering service) with Microsoft Exchange Online, it is essential to complete the following two configuration steps.


Failure to complete these steps can result in Exchange Online incorrectly identifying the source of inbound messages. This may affect anti-spam processing, spoof detection, and message authentication (SPF, DKIM, and DMARC), potentially leading to legitimate email being quarantined or rejected.


The required configuration consists of:

  1. Creating an Exchange Online inbound connector that only accepts email from Vitanium's mail filtering platform.

  2. Enabling Enhanced Filtering for Connectors (also known as Skip Listing) so Exchange Online correctly identifies the original sending server.

Step 1 – Create an Inbound Connector

Open the Exchange Admin Center

  1. Sign in to the Exchange Admin Center.

  2. Navigate to Mail Flow → Connectors.

  3. Select + Add a connector.

New connector

Configure the connector with the following settings:


SettingValue
Connection fromPartner organization
Connection toMicrosoft 365


Select Next.


Name

Enter the following:

Name: Vitanium Mail Filter


Select Next.


Authenticating sent email

Select:


By verifying that the sender domain matches one of the following domains


Enter the "*" wildcard to indicate to always use the connecter when receiving emails inbound. (Click +)


Select Next.


Security restrictions

Select 


Reject email messages if they aren't sent over TLS


and 


Reject email messages if they aren't sent from within this IP address range


Add the following Vitanium IP ranges:

  • 185.28.166.240/28

  • 109.74.252.0/26

  • 109.74.248.0/26


Select Next, then review the configuration.


Finally, select Create connector.

Step 2 – Enable Enhanced Filtering for Connectors

Enhanced Filtering ensures that Exchange Online evaluates the original sending IP address rather than the Vitanium filtering servers. This significantly improves spam detection accuracy and ensures SPF, DKIM, and DMARC validation operate correctly.

Configure Enhanced Filtering

  1. Navigate to:

    https://security.microsoft.com/skiplisting

  2. Select the Vitanium Mail Filter connector.

  3. Enable the following options:

    • Automatically detect and skip the last IP address

    • Apply to entire organization

  4. Save the configuration.

Validation

After completing both steps:

  • Exchange Online will only accept inbound mail delivered through the Vitanium Mail Filter.

  • Direct SMTP delivery from the Internet will be rejected.

  • Exchange Online will correctly identify the original sending IP address.

  • Microsoft Defender for Office 365 will perform more accurate anti-spam, anti-phishing, SPF, DKIM, and DMARC evaluation.

Vitanium IP Addresses

IP Range
185.28.166.240/28
109.74.252.0/26
109.74.248.0/26

References