DFO Default Anti-Spam (Outbound) policy exclusions

Nana Poku 345 Reputation points
2026-10-26T20:29:18.2566667+00:00

We have the default Anti-Spam policy configured, along with the custom Anti-spam policy targeting high-volume senders with a higher priority. We need to exclude a specific mailbox from being blocked and added the necessary exclusion. However, the mailbox is still being added to the Restricted entities list after sending bulk emails that exceed the configured threshold.

Could you appreciate any recommendations on how to prevent this mailbox from being restricted while maintaining the existing anti-spam protections for other users.

Microsoft 365 and Office | Microsoft 365 Defender | Other | Other
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  1. AI answer

    2026-10-26T20:29:35.63+00:00

    There isn’t a supported way to permanently exempt a mailbox from outbound spam restriction or the Restricted entities list while keeping outbound spam protection in place for everyone else.

    What can be done instead:

    1. Review the mailbox’s sending pattern in Exchange admin center
      • Use Message trace or delivery reports in the Exchange admin center (EAC) to confirm whether the mailbox is being blocked because it exceeded service sending limits or outbound spam policy thresholds.
    2. Use built-in alerts to monitor the mailbox earlier
      • The default alert policies User restricted from sending email, Email sending limit exceeded, and Suspicious email sending patterns detected notify admins when a sender is restricted or approaching problematic behavior.
    3. Reduce the chance of restriction by improving sender legitimacy
      • Configure SPF, DKIM, and DMARC for the sending domain.
      • Review message content and sending patterns, because large bursts and bulk-like traffic increase the chance of restriction.
    4. Use the right sending platform for bulk traffic
      • Exchange Online isn’t designed for bulk mailing scenarios. If this mailbox regularly sends bulk email, use a service designed for high-volume sending instead, such as Azure Communication Services Email, another bulk email provider, or an on-premises mail server for mass mailings.
      • For application-generated mail, consider SMTP relay via Microsoft 365 or Direct Send where appropriate, but these are still subject to Exchange Online sending limits.
    5. Keep anti-spam policy targeting specific and verify precedence
      • For anti-spam policies generally, only the first matching policy applies, based on priority. If overlapping policies exist, verify the intended mailbox is matched by the correct higher-priority custom policy and not by another policy first.
      • In Exchange Online PowerShell, this command can be used to review enabled anti-spam policy targeting:
         Get-HostedContentFilterRule | Where-Object {$_.State -eq 'Enabled'} | Format-Table Name, Priority, SentTo, SentToMemberOf, RecipientDomainIs

    For the stated scenario, the practical recommendation is to move that mailbox’s bulk sending workload off the normal Exchange Online mailbox path and onto a service intended for high-volume mail, while keeping the existing protections for standard users.

    References:

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