The enterprise telephony market is undergoing a radical transformation. According to the Gartner 2025 Magic Quadrant, 90% of organizations will rely on cloud platforms for their telephony by 2028, up from just 30% in 2025. Microsoft Teams, Zoom Phone, Cisco Webex: these UCaaS (Unified Communications as a Service) solutions are gradually replacing traditional PBX systems.
But this migration to the cloud raises a critical question for sales teams: what happens to your number reputation when you switch to Teams or Zoom telephony?
The problem: Your Teams calls marked as spam
The phenomenon is increasingly common. On Microsoft forums, testimonials are multiplying: "Our outgoing Teams calls are being seen as SPAM by our prospects," reports an IT administrator. The problem isn't new with traditional telephony, but cloud migration amplifies it for several reasons:
- Shared number pools: UCaaS providers sometimes assign numbers from ranges already used (and potentially already flagged)
- Incomplete Caller ID configuration: a poorly configured caller identification triggers spam filters
- Concentrated call volume: sales teams using the same platform create patterns detected as spam
- STIR/SHAKEN attestation: the attestation level depends on your tenant configuration
STIR/SHAKEN: The standard that changes everything
Since 2020, the STIR/SHAKEN framework (Secure Telephone Identity Revisited / Signature-based Handling of Asserted Information Using toKENs) has become the standard for call authentication. Essentially, each call receives a "signature" from the originating carrier, validated by the destination carrier.
The three attestation levels:
- Level A (Full Attestation): the carrier certifies that the caller has the right to use this number. Your calls display "Verified Caller"
- Level B (Partial): the customer is known but their right to use the number is not verified. Risk of "Possible Spam" display
- Level C (Gateway): no verification (e.g., international calls). "Possible Spam" display almost systematic
For your outbound calling campaigns, the goal is clear: obtain a Level A attestation.
Microsoft Teams Phone: Anti-spam solutions
Microsoft Teams remains the dominant UCaaS solution for organizations already in the Microsoft ecosystem. According to Gartner, its geographic coverage and AI features (transcription, predictive insights) make it a natural choice.
Recommended configuration
- Check Caller ID Policies: in Teams Admin Center > Voice > Calling policies, ensure your organization name and numbers are correctly configured
- Register your numbers: declare your numbers with identification registries (Free Caller Registry in the USA)
- Avoid excessive rotation: changing numbers during the day can trigger carrier spam filters
- Monitor your volumes: identical call patterns (same time, same duration) are detected as spam behavior
Known limitations
Microsoft doesn't yet offer native branded calling (displaying the company name on the recipient's phone). This highly requested feature is available from some competitors but absent from Teams Phone as of February 2026.
Zoom Phone: Advanced reputation management
Zoom has positioned itself as a complete cloud telephony player, with an anti-spam solution suite more comprehensive than the competition.
Key features
- Enterprise Spam Registration: license providing access to detailed spam score reports for each number
- Number Reputation Dashboard: dedicated dashboard to monitor your numbers' health in real-time
- Spam Remediation: integrated process to dispute false positives with anti-spam databases
- Branded Calling: display your verified company name on the recipient's phone
Integrated STIR/SHAKEN
Zoom Phone automatically displays the STIR/SHAKEN validation result on incoming calls:
- "Caller Signature Verified" = validated A attestation
- Neutral icon = B or C attestation
- "Caller NOT verified" = validation failed
For your outbound calls, Zoom automatically signs with the attestation level corresponding to your configuration.
Cisco Webex Calling: The enterprise approach
Cisco Webex targets large organizations and regulated sectors. Its spam management relies on STIR/SHAKEN with granular administrator controls.
Configuration via Control Hub
Webex administrators can:
- Automatically block calls whose Caller ID validation failed
- Choose to present unverified calls normally or with a "Possible Spam" indication
- Integrate third-party caller reputation providers (CCRP - Certified Caller Reputation Provider)
5 best practices to protect your cloud reputation
Regardless of your UCaaS platform, these recommendations apply:
- Audit your numbers before migration: check their current reputation on Truecaller, Hiya, etc. before transferring them to Teams or Zoom. Our crisis management guide details the verification steps.
- Configure Caller ID correctly: complete company name, verified main number, no temporary numbers
- Register your numbers: register them with official registries (Free Caller Registry in the USA, European equivalents being deployed)
- Monitor continuously: use native dashboards (Zoom) or third-party tools to detect reputation degradation. Our verification API allows automating this monitoring.
- Anticipate regulations: STIR/SHAKEN is mandatory in the USA and Canada. Europe is preparing equivalents. Be ready with compliant configurations now.
Cloud vs traditional telephony: The verdict
Cloud telephony is neither better nor worse than traditional telephony for reputation. It's different:
| Aspect | Traditional telephony | UCaaS (Teams/Zoom) |
|---|---|---|
| Number control | Full (you own them) | Partial (depends on provider) |
| STIR/SHAKEN | Manual configuration required | Often natively integrated |
| Reputation monitoring | External tools only | Integrated dashboards (Zoom) |
| Branded calling | Via carrier | Depends on platform (Zoom yes, Teams no) |
| Responsiveness in case of blacklist | Depends on carrier | Integrated remediation processes |
FAQ
Why are my Teams calls marked as spam when it wasn't the case with my old system?
Several factors: numbers from recycled pools, incomplete Caller ID configuration, or STIR/SHAKEN attestation at level B or C instead of A. Check your settings in the Teams Admin Center and contact your number provider to obtain a Level A attestation.
Is Zoom Phone better equipped than Teams to manage reputation?
As of February 2026, Zoom does offer more advanced features: dedicated reputation dashboard, branded calling, integrated remediation process. Microsoft Teams Phone remains more limited on these specific aspects, even though the platform suits organizations prioritizing integration with the Microsoft 365 ecosystem.
Does STIR/SHAKEN work in Europe?
STIR/SHAKEN is mandatory in the United States and Canada. In France and Europe, the framework is not yet deployed but similar initiatives are being prepared. The French MAN (Number Authentication Mechanism) should integrate equivalent principles in the coming years.
Can I use HUHU to monitor my Teams or Zoom numbers?
Absolutely. Our verification API works independently of your telephony infrastructure. Whether your numbers are on Teams, Zoom, a traditional PBX, or a mobile carrier, you can check their reputation and receive real-time alerts.
For a comprehensive approach to securing your VoIP infrastructure, check our SIP trunking and phone reputation technical guide — it covers essential SBC, encryption, and monitoring best practices for IT directors.
