What are Microsoft SCL and BCL ratings and how do they affect email deliverability?
Updated on 4 Oct 2026: We updated this guide for Microsoft's current SCL guidance and Outlook Promotions handling.
Microsoft SCL and BCL are separate ratings. SCL means spam confidence level, a value stamped on an individual message. BCL means bulk complaint level, a value that describes bulk sender complaint behavior. In Microsoft 365 cloud mailboxes, the filtering category, recipient policy, and any overrides determine how a message is handled. SCL alone does not determine the spam verdict or delivery action.
The practical answer is this: use SCL as one diagnostic signal and BCL to assess bulk classification against the recipient tenant's threshold. Neither rating maps cleanly to only domain reputation or only IP reputation. The visible From domain, authenticated domains, sending IP, message content, list quality, recipient feedback, and the recipient tenant's settings all matter.
- SCL: Low values such as 0 or 1 usually accompany mail assessed as nonspam, but the value alone does not establish placement.
- BCL: A BCL of 5 describes a bulk sender with a mixed level of complaints.
- Deliverability: The applied BCL threshold, filtering category, and policy action determine whether bulk mail reaches the Inbox, Junk Email, or quarantine.
- Diagnosis: Start with full headers, especially CAT, SRV, and SFV, then confirm the applied policy and delivery result.
How SCL works
Microsoft describes SCL as a value stamped on messages after spam analysis. The Microsoft SCL page explains that its historical role was to indicate whether mail looked good or bad. In cloud mailboxes, SCL no longer determines whether a message receives a Spam or High confidence spam verdict, or which action is taken. The same SCL can accompany different filtering outcomes.
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|---|---|---|
-1 | Spam filtering bypass requested or skipped | The stamped value can differ from the bypass request. |
0, 1 | Usually assessed as nonspam | Check CAT, SFV, overrides, and delivery action. |
5, 6 | Historically associated with spam | The filtering category and policy control the action. |
7, 8, 9 | Higher historical spam confidence | Do not infer the final verdict from SCL alone. |
How to read SCL values without assuming a cloud delivery action.
Find SCL in the X-Forefront-Antispam-Report header. CAT identifies the filtering category, such as BULK or SPM, and SRV:BULK indicates bulk detection at the applied threshold. SFV helps explain the spam filtering result or an override. These fields and the recipient's delivery result are more useful than interpreting the SCL number alone.
SCL is not a raw complaint rate
Complaints can affect sender reputation, but SCL is a message header value, not a sender complaint percentage. Mail flow rules can request an SCL setting, and other filtering or overrides can affect the result. In cloud mailboxes, read SCL alongside CAT, SFV, the applied policy, and the actual delivery action.
How BCL works
BCL is narrower. It describes bulk email, also called gray mail, and how complaint-prone that bulk sender appears. The Microsoft BCL page says Microsoft 365 assigns BCL values to inbound messages from bulk senders. Higher BCL means the bulk message is more likely to show unwanted spam-like behavior.
BCL interpretation bands
Microsoft BCL values describe whether mail is bulk and how complaint-prone the sender appears.
Not bulk
0
The message is not from a bulk sender.
Few complaints
1-3
The message is from a bulk sender with a low complaint pattern.
Mixed complaints
4-7
The message is from a bulk sender with mixed complaint behavior.
High complaints
8-9
The message is from a bulk sender with a high complaint pattern.
BCL filtering depends on the receiving Microsoft 365 tenant. The default anti-spam policy threshold is 7, the Standard preset threshold is 6, and the Strict preset threshold is 5. A value that meets or exceeds the threshold triggers the configured bulk action when bulk-spam marking is on. Default, new, and Standard policies send this mail to Junk Email by default; Strict quarantines it.
Example Microsoft message headerstext
X-MS-Exchange-Organization-SCL: 1 X-Microsoft-Antispam: BCL:5; Authentication-Results: spf=pass dkim=pass dmarc=pass
Those headers say the message authenticated, has SCL 1, and received BCL 5. They do not establish the filtering category or delivery action. Check CAT and SRV in X-Forefront-Antispam-Report, the recipient's policy, and the actual delivery result before attributing placement to BCL.
How the BCL threshold affects placement
SCL and BCL are separate values, but the BCL threshold can produce a Bulk filtering verdict. When a message meets the applied threshold and MarkAsSpamBulkMail is on, as it is by default, Microsoft applies the configured bulk action. In cloud mailboxes, do not assume a particular SCL value is required for that action.
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|
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|---|---|---|
Default or new | 7 | Below threshold; no threshold-based bulk action. |
Standard | 6 | Below threshold; no threshold-based bulk action. |
Strict | 5 | Threshold met; quarantine by default if bulk-spam marking is on. |
Custom | Administrator selected | Compare the value with the threshold and configured action. |
How the built-in policy thresholds treat a message with BCL 5.
Read the filtering category with the applied policy
If a captured message shows SCL 1 and BCL 5, do not infer its placement from those numbers. Check CAT:BULK and SRV:BULK, then confirm the recipient's threshold, bulk action, policy assignment, and any override in the email entity page or message trace.
Where the Promotions folder fits
The Microsoft BCL page says messages identified as bulk now receive a Promotions tag, regardless of their BCL value. For supported Outlook clients, an administrator can turn on Bulk moves enabled in the anti-spam policy to move bulk mail that would otherwise reach the Inbox into the Promotions folder. This setting is off in Standard and Strict preset policies, and Microsoft still labels the setting Preview in its policy instructions.
The Promotions tag does not mean the BCL threshold was met. Mail at or above the threshold still receives the configured bulk action, such as Junk Email or quarantine. Even a message with BCL 0 can receive a Promotions tag if Microsoft identifies it as bulk, so compare the tag with the policy and final folder before diagnosing a deliverability drop. The earlier Preview mail flow rule that added the Bulk tag is no longer required.
Why SCL and BCL can differ
SCL and BCL describe different aspects of a message. SCL is a spam confidence value stamped in the header. BCL describes whether Microsoft sees bulk mail and how complaint-prone that bulk sender appears. An authenticated newsletter can have SCL 1 and BCL 5. Whether it receives a Bulk verdict and a bulk action depends on the applied threshold and policy.
Flowchart showing separate SCL and BCL classification paths.
When spam filtering flags mail
- Content: The message body, links, wording, or attachment pattern can contribute to a spam verdict.
- Authentication: SPF, DKIM, or DMARC failure can raise suspicion.
- Policy: A mail flow rule, tenant setting, or override can affect the result.
When BCL is high
- Bulk status: Microsoft recognizes the sender or message stream as bulk mail.
- Complaints: The bulk sender pattern has enough complaints to raise the rating.
- Threshold: The recipient tenant filters bulk mail at its configured BCL level.
Microsoft destinations can behave differently from other mailbox providers because recipient tenants can apply different bulk thresholds and actions. A sender can look clean elsewhere and still have a Microsoft-specific bulk filtering problem.
Is it the IP, domain, or message?
SCL and BCL do not give you a one-field root cause. Separate the investigation into the mail being sent, the sending identity, and the infrastructure. Shared IP ranges deserve attention, especially when the sender has Microsoft-only problems, but a questionable IP range does not automatically explain BCL 5.
A real test message matters more than a dashboard screenshot. Send the same campaign seed to Microsoft 365 and non-Microsoft inboxes, inspect the full headers, and compare SCL, BCL, CAT, authentication, and final folder placement. Suped's email tester supports that workflow with one report for authentication, content, and placement signals.
Email tester
Send a real email to this address. Suped shows a results button when the test is ready.
?/43tests passed
Then look for patterns. If all mail from one shared IP family has Microsoft trouble, infrastructure is a lead. If only one newsletter stream has BCL issues, investigate audience fit, complaint behavior, cadence, and content. If transactional mail and marketing mail share a domain, separate the streams before drawing conclusions.
- IP evidence: Multiple unrelated senders on the same range have Microsoft-only filtering trouble.
- Domain evidence: All mail using the same visible From domain has higher junk placement.
- Message evidence: Only one template, campaign type, or list segment receives the bad rating.
- Tenant evidence: The same message lands differently across Microsoft 365 recipients.
How to troubleshoot Microsoft SCL and BCL
Capture evidence before changing anything. Keep the raw headers, sending stream, domain, IP, authentication results, filtering category, applied policy, and recipient outcome together. SCL or BCL alone cannot identify the cause.
Microsoft Defender portal report view with SCL and BCL filtering controls.
- Collect headers: Get the original headers from a Microsoft 365 recipient. Record SCL, BCL in X-Microsoft-Antispam, CAT and SRV in X-Forefront-Antispam-Report, SFV, authentication results, and the final folder.
- Identify the decision source: Use the email entity page or message trace to check the filtering category, mail flow rules, connection filtering, policy settings, and user or tenant overrides. CAT:BULK with SRV:BULK points to threshold-based bulk filtering.
- Verify authentication: Confirm SPF or DKIM passes and aligns with the visible From domain so DMARC passes. Use DMARC monitoring to find failing sources.
- Check reputation: Review IP and domain blocklist or blacklist exposure with blocklist monitoring, especially for shared IP ranges.
- Segment results: Compare newsletters, transactional messages, lifecycle messages, and one-to-one mail separately.
- Test one variable: Change the subject, template, link domain, audience segment, or sending cadence, then capture another Microsoft result.
- Escalate false positives: If authentication passes and no local policy explains the result, ask the recipient admin to submit the original message to Microsoft for analysis.
Minimal DMARC record during monitoringtext
v=DMARC1; p=none; rua=mailto:reports@yourdomain.com
That DMARC record does not lower BCL by itself. It requests aggregate reports, provided the report address is set up to receive them. Once you know which sources pass or fail, move toward a stricter policy in controlled stages. Authentication problems are easier to fix when each source is visible instead of treating every Microsoft junk placement as one generic issue.
What to change when BCL is high
When BCL is high but the message is otherwise not classified as spam, start with the sender's bulk pattern. Microsoft is identifying a bulk stream with mixed or high complaint behavior. Fix the conditions that make recipients report the mail as junk or treat it as unwanted.
Good bulk mail still needs restraint
Bulk does not mean bad. It means one sender is sending similar messages to many recipients. An opted-in newsletter can still earn complaints if the topic, frequency, sender identity, or unsubscribe path does not match recipient expectations.
- List quality: Suppress inactive recipients and remove addresses that never engage with Microsoft mailboxes.
- Expectation match: Make the sender name, subject, and first screen match what the subscriber asked to receive.
- Unsubscribe path: Make leaving the list easier than reporting the message as junk.
- Stream separation: Separate newsletters, product updates, receipts, and support mail by subdomain and sending stream.
- Volume control: Reduce frequency for recipients who stop opening or clicking, especially at Microsoft domains.
- IP hygiene: Move away from shared infrastructure when neighboring senders keep creating Microsoft reputation issues.
If the filtering category shows spam rather than bulk, widen the investigation. Content, authentication, DMARC policy, link reputation, malware, or spoofing signals need attention. The SCL headers view is useful when header values do not match the final folder placement.
Where Suped fits
Suped cannot force Microsoft to lower an SCL or BCL value. Suped's product helps with sender-controlled work: checking authentication, finding broken sources, monitoring DMARC policy, spotting SPF and DKIM problems, watching blocklist and blacklist exposure, and turning report data into fixes.
DMARC record detail view showing SPF, DKIM, DMARC, rDNS diagnostics, and DNS records
Suped connects DMARC, SPF, DKIM, hosted policy controls, blocklist monitoring, and real-time alerts in one workflow. This helps a team rule out authentication and sender setup problems before attributing Microsoft filtering to content, audience behavior, or recipient policy.
Use Suped to keep the evidence clean
- Issues: Automated detection points you to failing sources and the steps to fix them.
- Alerts: Real-time alerts help you catch authentication failures before they become a wider deliverability problem.
- MSP scale: Multi-tenancy keeps client domains, reports, and sender sources organized.
- DNS control: Hosted SPF and hosted DMARC reduce repeated DNS changes during policy staging.
If the main issue is BCL, Suped helps rule out avoidable technical causes first. The remaining work is list quality, recipient expectation, content fit, and Microsoft-specific sending history. For high BCL cases, this high BCL fixes page goes deeper into that path.
Views from the trenches
Best practices
Capture full Microsoft headers before changing DNS, content, or the sending platform.
Separate bulk streams from transactional mail so ratings do not blur distinct causes.
Compare BCL thresholds across tenants before declaring a universal Microsoft issue.
Common pitfalls
Treating BCL as an IP-only score misses content, audience, and complaint signals.
Assuming SCL 1 means no risk ignores tenant bulk settings and BCL enforcement rules.
Using shared IPs without monitoring neighboring reputation can hide Microsoft risks.
Expert tips
Track SCL, BCL, authentication, and folder placement together for every seed test.
Use a dedicated newsletter subdomain when bulk mail differs from core business mail.
Fix list fatigue before template polish when BCL rises and SCL stays consistently low.
Expert view
Expert from Email Geeks says SCL measures how likely Microsoft thinks a message is spam, while BCL identifies bulk mail and the complaint pattern behind that bulk stream.
2023-10-23 - Email Geeks
Marketer view
Marketer from Email Geeks says BCL enforcement depends on the recipient tenant, so the same BCL value can pass one Microsoft 365 organization and hit junk in another.
2023-10-23 - Email Geeks
The practical takeaway
SCL and BCL describe different parts of Microsoft filtering. In cloud mailboxes, SCL is a header value, while CAT and related signals show the filtering verdict. BCL describes bulk sender complaint behavior. Meeting the recipient tenant's BCL threshold can produce a Bulk verdict and the configured bulk action when bulk-spam marking is on.
When you see SCL 1 and BCL 5, read it as a low SCL with a mixed-complaint bulk rating. Check CAT, SRV, the applied policy, and the final folder before naming the placement cause. Fix authentication, DMARC visibility, and sending stream separation where needed. For a Bulk verdict, reduce unwanted mail through better list quality, relevance, unsubscribe handling, and sending cadence.
