Email blocked from sending

Andrew Hughes 0 Reputation points
2026-09-30T10:51:13.5366667+00:00

On on my team using [Moderator note: Personally Identifiable Information removed] @pdln.info sent messages to our mailing list yesterday. They inadvertently exceeded the 500 limit, and one recipient put the message in junk. The email has now been blocked and we cant now perform normal business work using it. How can we remove that block on that email. Obviously we will stay within the 500 daily limit in future. This is business critical for my company [Moderator note: Personally Identifiable Information removed] and we will have to move if we cant resolve this.

Microsoft 365 and Office | Install, redeem, activate | For business | Windows
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  1. AI answer

    2026-09-30T10:51:28.9333333+00:00

    A blocked Microsoft 365 sender can usually be restored by an admin from the Restricted entities page, but the account should be checked first for compromise or spam-like activity before unblocking it.

    1. In the Microsoft Defender portal, open Restricted entities at https://security.microsoft.com/restrictedusers.
    2. Confirm the affected mailbox appears there. A blocked sender typically also gets NDR 550 5.1.8 Access denied, bad outbound sender.
    3. Before removing the block, verify why it happened:
      • Check sign-in logs for suspicious activity.
      • Check for unknown inbox rules or forwarding rules.
      • Review recent sent items to confirm the messages were legitimate.
    4. If the account was not compromised, remove the user from Restricted entities.
    5. Allow time for the restriction to clear after unblocking.

    To reduce the chance of this happening again:

    • If this mailbox is being used for bulk or list mail, use bulk-sender practices instead of sending all messages at once.
    • Spread sends over time and do not exceed 30 messages per minute per mailbox.
    • Maintain list hygiene and include a working unsubscribe option for bulk mail.
    • Configure outbound spam policies with appropriate per-hour and daily limits and notifications.
    • Make sure Email sending limit exceeded alert policies are enabled.
    • Enable MFA on the account.
    • Review mail flow reports and message traces periodically.

    There is no documented permanent ignore/exemption on the Restricted entities page. The documented approach is to investigate the cause, unblock the user, and prevent recurrence with outbound spam policy and bulk-sending practices.

    References:

    AI-generated content may be incorrect. Read our transparency notes for more information.

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  2. Killian N 4,330 Reputation points Independent Advisor
    2026-09-30T13:12:47.35+00:00

    Hi Andrew

    If this is a Microsoft 365 business mailbox, an administrator should first check whether the affected account appears under Restricted entities in the Microsoft Defender portal. Microsoft places accounts there when outbound sending limits are exceeded or suspicious sending activity is detected.

    Please ask your organization's IT admin to:

    1. Open the https://security.microsoft.com/restrictedentities.
    2. Locate and select the affected mailbox.
    3. Select Unblock.
    4. Review the security recommendations, confirm that the account has not been compromised, and then submit the request.

    Before removing the restriction, the administrator should review recent sign-ins, Sent Items, inbox rules, and forwarding rules for anything unfamiliar. If suspicious activity is found, the password should be reset and multifactor authentication enabled before unblocking the account.

    The exact non-delivery report is also important. For example, 550 5.1.8 Access denied, bad outbound sender normally indicates that the individual sender has been restricted.

    Please also note that 500 recipients is the default limit per individual message, not the daily recipient limit. Exchange Online separately applies other per-user and organizational limits. For recurring mailing-list or bulk communication, Microsoft recommends using a service designed for high-volume email rather than a normal Microsoft 365 mailbox.

    You can find the complete instructions here:

    I hope this helps you restore normal sending as quickly as possible.

    Kind regards,

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