MailFixIt

Outlook SMTP delivery response

Understand Outlook 550 5.7.502: Sender banned

Microsoft banned the sending account because its systems detected spam activity.

Problem description

A representative response is:

550 5.7.502 Sender banned.
Is this temporary or permanent?

Stop sending and secure the account before requesting restoration from Microsoft.

What this response means

550 5.7.502 Access denied, banned sender means Microsoft has banned the sending account after detected spam activity. It is not a routine DNS failure.

Fix it

  1. Stop sending from the affected account and pause any application that uses it.
  2. Review sign-ins, sessions, inbox rules, forwarding, OAuth applications, sent items, and outbound logs for compromise.
  3. Revoke sessions and tokens, reset credentials, require strong multifactor authentication, and remove malicious rules or integrations.
  4. Correct the mailing practice or automation that produced abusive traffic.
  5. Contact Microsoft Support through the tenant’s normal channel with the full NDR, account, timestamps, and the remediation already completed.

Do not bypass the ban with another account. That can spread the incident and trigger more restrictions.

What MailFixIt can check

MailFixIt can review public SPF, DKIM, and DMARC as supporting configuration. It cannot inspect or restore a banned Microsoft account.

After Microsoft restores access, send a small controlled test and monitor the account before resuming normal volume.

Frequently asked questions

What does Outlook 550 5.7.502: Sender banned mean?

Microsoft banned the sending account after detecting spam activity. Secure and remediate the account before asking Microsoft to restore sending.

Can MailFixIt prove this entire bounce from public DNS?

No. The current checker can evaluate selected public DNS configuration, but it cannot recreate recipient state, credentials, reputation, message content, or a historical provider SMTP decision.

Related email diagnostics

Outlook 550 5.7.515: Access denied, sending domain does not meet the required authentication levelDiagnose Outlook 550 5.7.515 email rejection safely. Check SPF, DKIM and DMARC DNS, interpret the receiver report, and identify the next configuration step. Outlook.com requirements for high-volume sendersCheck Outlook.com high-volume sender requirements for SPF, DKIM and DMARC alignment, then review sending-IP PTR as separate infrastructure evidence.

Primary sources: Microsoft 365 non-delivery reports.