What the bounce says
Exact wording as it appears in the rejection or NDR. Placeholders such as x.x.x.x and example.com stand for your own address and domain.
550 SC-004 Mail rejected by Outlook.com for policy reasons. A block has been placed against your IP address because we have received complaints concerning mail coming from that IP address. We recommend enrolling in our Junk Email Reporting Program (JMRP).
SC-004 is a complaint-driven block: enough Outlook.com users marked mail from this IP as junk that Microsoft stopped accepting it. The text recommends JMRP because complaint feedback is the tool that prevents recurrence.
Most common causes
- Recipients did not expect the mail or could not unsubscribe
- Purchased or scraped lists
- Misleading subject lines or sender names
- High frequency to disengaged recipients
What to verify next
- Enrol in JMRP to receive complaint feedback and suppress complainers
- Confirm opt-in for the list and remove unengaged recipients
- Make unsubscribe one-click and honour it immediately
- Reduce frequency and request review once complaints fall
Why people complain
They did not sign up, they signed up long ago and forgot, they cannot find the unsubscribe link, or the mail is too frequent. Complaint rates rise sharply on purchased lists and on re-engagement campaigns to dormant addresses.
Microsoft’s tolerance is low; a small percentage of complaints across a send is enough for a block on a low-volume IP.
- Consent and expectation drive complaints.
- One-click unsubscribe reduces them.
- Dormant addresses complain most.
Fix list and process
Enrol in JMRP and suppress every complainer immediately. Implement one-click unsubscribe in headers and honour it instantly. Remove recipients who have not engaged for months. Reduce frequency.
Request review
After changes are live, submit to sender support. Complaint-based blocks lift as the complaint rate falls, so continued clean sending matters more than the request itself.
Best diagnostic path
Mail Failure Doctor
Classify the complete rejection and preserve provider-specific diagnostic context.
Open analysis → Live analysisEmail Infrastructure Digital Twin
Map the domain’s public mail infrastructure and provider relationships before remediation.
Open analysis →Known limits
- Complaint rates are only visible through JMRP.
- Recovery depends on future sends, not on the request alone.
Common questions
How many complaints trigger SC-004?
Microsoft does not publish a number; the rate relative to volume is what matters.
Does JMRP cost anything?
No. It is free and sends a copy of each complaint to a mailbox you specify.
Can I resend to the same list?
Not until complainers and dormant addresses are removed; otherwise the block returns.
Why the exact message matters
The same status family can be triggered by different conditions, and providers frequently add diagnostic text that narrows the issue. Use the complete rejection text rather than treating the numeric code as a complete diagnosis.
Provider reference
For the provider-defined meaning and current requirements, review Microsoft Outlook.com sender troubleshooting.