outgoing emails are being blocked from sending

Question

My outgoing emails on a distribution list are not being sent because they are being identified as suspected spam

Answer 1

Hello

Are you using an outlook.com or hotmail.com address, or is this a business email address?

How many are you including in the To, cc or bcc field?

Answer 2

When outgoing messages are blocked as suspected spam, the sending account or address is typically being throttled or restricted by Microsoft’s outbound spam protection.

For Outlook.com or Microsoft 365-based sending, use these steps:

1. Check whether the sender has been restricted
   • If the sender is part of a Microsoft 365 organization, an admin should:
     • Go to the Microsoft 365 Defender portal → Restricted entities page (https://security.microsoft.com/restrictedusers).
     • Look for the affected user or distribution-related account and unblock it if present.
     • After unblocking, sending is usually restored within about an hour.
   • This restriction can occur if sending limits are exceeded or if the account is detected sending spam.
2. Secure any potentially compromised account
   • If there is any sign that a member account or the sending account is compromised (unexpected mail, unusual sign-in locations, or large volumes of outbound mail), follow the guidance to secure the account and reset credentials before resuming normal sending.
3. Review outbound spam controls and alerts (for admins)
   • In Microsoft 365, outbound spam protection automatically:
     • Monitors accounts that send too much spam or too many messages too quickly.
     • Blocks those accounts from sending when internal thresholds are exceeded.
   • Admins should review:
     • Alert policies such as User restricted from sending email, Email sending limit exceeded, and Suspicious email sending patterns detected in the Defender portal.
     • Message trace or delivery reports in the Exchange admin center to confirm that messages from the distribution list are being blocked as spam.
4. Improve sender reputation and sending patterns
   • Ensure that:
     • Messages are not bulk-like or unsolicited.
     • Content does not resemble phishing or spam (suspicious links, misleading subjects, etc.).
     • Members of the distribution list are legitimate recipients who expect the mail.
   • For external deliverability issues (messages to Outlook.com/Hotmail/MSN/Live recipients being treated as spam), verify that sending IPs and domains comply with Microsoft sender policies and, if still blocked, use the Outlook.com sender support form referenced in the documentation to request assistance.
5. If messages are still blocked
   • For Outlook.com consumer accounts, if deliverability problems persist even after confirming that messages are legitimate and accounts are secure, contact Outlook.com sender support using the troubleshooting form referenced in the sender support article so Microsoft can review the sending pattern and adjust reputation if appropriate.

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References:

• NDR error code "550 5.1.8 Access denied, bad outbound sender"
• Sender Support in Outlook.com
• Outbound spam protection for cloud mailboxes