Skip to content
Better Sharing Better Sharing

Referral Feature Architecture

Subtitle: A Technical Blueprint for Building Privacy-Compliant Referral Systems

Designing a privacy-compliant referral program isn’t just about wording opt-ins and privacy policies correctly.
It’s about engineering your systems to minimize risk from the first API call to the last invite email.

Your code is your first—and best—privacy firewall. The architectural decisions you make when building referral features will determine how effectively you can protect user data, maintain compliance, and build sustainable growth.

This article shows developers and product teams how to architect referral systems that process contact data ethically, securely, and legally, with specific implementation guidance for each component.

Core Foundation

This article builds from:
How to Handle Contacts Without Breaking Privacy Laws

Supporting articles:

Core Principles for Referral Feature Architecture

The foundation of privacy-compliant referral systems rests on several key architectural principles that should guide your implementation decisions:

Principle Application Implementation Guidance
Data minimization Only import/process fields you need Limit API scopes; collect only email and name if necessary; avoid storing unnecessary metadata
User-driven action Manual contact selection and invite confirmation Require explicit user actions; avoid auto-selection; implement clear confirmation steps
Transparency Message previews + disclosure footers Show users exactly what will be sent; include all required disclosures; make commercial nature clear
Opt-out enforcement Global suppression lists Implement centralized suppression database; check before sending any message; honor opt-outs across users
Retention limits Short-term storage of unmatched contacts Set automatic deletion timers; document retention policies; minimize storage duration

These principles should be embedded in every aspect of your referral system architecture, from the initial contact import to the final message delivery and beyond.

Step-by-Step Technical Design

1. Contact Import Handling

The contact import process is the first critical touchpoint where privacy risks can be introduced or mitigated. A well-designed import system minimizes data collection and server-side processing.

Key Implementation Requirements:

  • Use OAuth with least-privileged scopes (e.g., contacts.readonly)
  • Only fetch emailAddresses (and name if absolutely needed)
  • Import contacts client-side when possible
  • Avoid persisting full contact lists server-side unless necessary

Implementation Guidance:

When integrating with contact providers (Google, Microsoft, etc.), request only the minimum necessary permissions. For example, with Google People API:

GET /people/me/connections?personFields=emailAddresses,names

This retrieves only email addresses and names, not phone numbers, addresses, or other personal information.

Privacy-Forward Design Pattern:

Consider implementing a client-side contact selector that:

  1. Fetches contacts directly in the user’s browser
  2. Allows selection without sending the full list to your servers
  3. Only transmits the specifically selected contacts when the user confirms

This approach significantly reduces your data footprint and associated compliance obligations.

2. Contact Selection UX and API

The contact selection interface is where users make critical decisions about sharing their contacts’ information. This component must be designed to encourage deliberate, informed choices.

Key Implementation Requirements:

  • Allow users to manually select contacts to invite
  • Default selection state = 0 contacts selected (no pre-checked boxes)
  • Show:
    • Contact email
    • (Optional) First name
  • No auto-invites, no mass selects without confirmation

Implementation Guidance:

Design your contact selection interface to:

  • Present a clear, scrollable list of contacts
  • Require individual selection (checkboxes or similar)
  • Avoid “Select All” options that might encourage mass invitations
  • Include clear messaging about what will happen when contacts are invited

User Experience Considerations:

  • Provide search/filter functionality for large contact lists
  • Group contacts by domain or other relevant attributes
  • Show the number of selected contacts prominently
  • Include preview functionality so users can see what their contacts will receive

3. Consent Capture Before Sending

Capturing and documenting user consent is essential for both legal compliance and establishing a clear audit trail of user actions.

Key Implementation Requirements:

  • Insert explicit user action (e.g., a “Send Invites” button)
  • Include a consent checkbox with clear language: 
    □ I confirm I have permission to invite these contacts.
  • Log consent event with:
    • User ID
    • Timestamp
    • Contacts selected (hashed)
    • Message version
    • Consent text shown
    • User’s IP address (for verification purposes)

Implementation Guidance:

The consent capture system should:

  • Prevent form submission if the consent checkbox is not checked
  • Store consent records in a secure, tamper-evident database
  • Include the exact text of the consent statement shown to the user
  • Be designed to produce verifiable records if needed for regulatory inquiries

Legal Considerations:

Different jurisdictions have varying requirements for valid consent. Your system should be flexible enough to:

  • Display different consent language based on user location
  • Capture additional consent elements for high-risk regions
  • Maintain records for the duration required by applicable laws

4. Invitation Messaging Engine

The messaging engine handles the actual delivery of invitations and must be designed to ensure compliance with various marketing and privacy regulations.

Key Implementation Requirements:

  • Route outbound invites through a transactional email system (e.g., SendGrid, Postmark)
  • Always include:
    • Sender identity (both user and platform)
    • Reason for the invite
    • Opt-out link
    • Privacy policy link
    • Any required disclosures about incentives

Implementation Guidance:

Example message structure:

Subject: [User Name] invited you to join [Platform]

Hi [Recipient Name],

[User Name] thought you might be interested in [Platform].
[Optional: personalized message from user]

[Platform] helps you [brief value proposition].

[Call to action button]

---

You were invited by [User Name] to try [Platform].
If you'd prefer not to receive future invites, [unsubscribe here].
[Company Name, Address]
[Privacy Policy Link]

Compliance Considerations:

  • Ensure all required sender information is included (especially important for CAN-SPAM and CASL)
  • Make opt-out mechanisms prominent and functional
  • Include any required disclosures about incentives or rewards
  • Ensure the message clearly identifies both the referring user and your platform

5. Suppression and Unsubscribe Management

A robust suppression system is critical for honoring recipient preferences and maintaining compliance with opt-out requirements.

Key Implementation Requirements:

  • Hash invitee emails (e.g., SHA-256)
  • Store hashes in a global suppression list
  • Apply suppression checks before sending any future invites
  • Allow immediate opt-outs from all users’ invites, not just the original sender

Implementation Guidance:

The suppression system should:

  • Check all outbound invitations against the suppression list before sending
  • Process opt-outs immediately (within 24 hours at most)
  • Apply opt-outs globally across all users and campaigns
  • Maintain suppression records indefinitely or for the maximum required period

Technical Design Considerations:

  • Use consistent hashing algorithms for suppression list entries
  • Implement database indexes for fast suppression checks
  • Consider bloom filters or similar data structures for efficient matching
  • Include timestamp and reason for each suppression entry

6. Retention and Deletion Policies

Proper data retention policies minimize risk by ensuring that personal data is kept only as long as necessary for legitimate purposes.

Key Implementation Requirements:

Data Type Retention Window Implementation Approach
Uninvited contacts Delete after session ends Temporary client-side storage; no server persistence
Invited contacts (not signed up) Retain for 30–60 days Store hashed for suppression purposes; set automatic deletion
Suppressed contacts Retain hashed data indefinitely Store only hashed values; document purpose for retention

Implementation Guidance:

Your retention system should:

  • Implement automatic deletion workflows based on configurable timeframes
  • Document the purpose and legal basis for each retention period
  • Include mechanisms for handling data subject deletion requests
  • Maintain audit logs of deletion activities

Risk Mitigation Approach:

  • Store only hashed versions of contact data when possible
  • Implement data partitioning to separate identification data from usage data
  • Consider pseudonymization techniques for necessary long-term storage
  • Document your retention decisions and their legal basis

7. Logging and Audit Trails

Comprehensive logging creates accountability and provides evidence of compliance with privacy regulations.

Key Implementation Requirements:

  • Log every invite event:
    • Sender ID
    • Recipient email (hashed)
    • Consent checkbox status
    • Timestamp
    • Message version
    • Unsubscribe events

Implementation Guidance:

Your logging system should:

  • Store logs securely with appropriate access controls
  • Implement tamper-evident logging mechanisms
  • Include sufficient detail for regulatory inquiries
  • Maintain logs for the period required by applicable regulations

Security Considerations:

  • Encrypt sensitive log data
  • Implement access controls for log viewing
  • Consider log integrity verification mechanisms
  • Establish retention periods for logs based on regulatory requirements

Design Pattern Examples

Implementing these principles correctly requires careful attention to both the user experience and the underlying technical architecture. Here are examples of good and bad practices:

Component Good Practice Bad Practice Implementation Guidance
Invite Button Requires selection + consent One-click “Invite All” Implement multi-step confirmation; show preview before sending
API POST /invite Requires hashed recipient list Raw emails stored Hash emails before transmission; minimize data fields
Suppression Check Before message queue enqueue After sending attempt Implement pre-send validation; check at multiple points
Retention Policy Auto-delete unmatched contacts Keep all imports forever Set deletion timers; document retention periods
Contact Import Client-side processing Server-side processing Use client-side OAuth; minimize server data exposure
Consent Capture Explicit checkbox + button Pre-checked box or no consent Require affirmative action; store consent records

Global Privacy Alignment

Following this architecture ensures compliance with major privacy regulations worldwide:

  • GDPR (EU/UK) – Article 25 (Data Protection by Design and by Default)

    • Implements data minimization principles
    • Provides clear consent mechanisms
    • Enables data subject rights fulfillment
    • Documents processing activities

  • CPRA (California) – Data minimization and opt-out of data sharing

    • Honors “Do Not Sell or Share” requirements
    • Implements appropriate retention periods
    • Provides transparency about data use
    • Enables deletion rights

  • CASL (Canada) – Express consent and suppression enforcement

    • Captures and documents express consent
    • Implements immediate unsubscribe functionality
    • Maintains records of consent
    • Honors opt-outs globally

  • CAN-SPAM (USA) – One-click opt-out and sender disclosure

    • Includes required sender information
    • Provides simple opt-out mechanisms
    • Honors opt-outs promptly
    • Avoids deceptive practices

  • LGPD (Brazil) – Data subject rights and proportionality

    • Implements appropriate security measures
    • Enables data subject rights fulfillment
    • Documents lawful basis for processing
    • Applies data minimization principles

For more detailed information on specific regulatory requirements, see: Other Privacy Laws

Summary: Architecture = Protection

A well-designed referral system architecture doesn’t just facilitate compliance—it builds trust, reduces risk, and creates sustainable growth opportunities.

Engineering Principle Privacy Outcome Business Benefit
Minimal contact collection Lower data breach risk Reduced security liability
Explicit consent before sending Higher user trust Better sender reputation
One-time, user-initiated invites Compliance with marketing laws Fewer spam complaints
Hashing + suppression Honor non-user rights globally Improved deliverability
Audit trails Faster regulatory responses Simplified compliance reporting

If you design privacy-first systems, you don’t just protect your users—you protect your roadmap. Privacy-forward architecture reduces regulatory risk, builds user trust, and creates sustainable growth channels that won’t be disrupted by future privacy changes.

Up Next

Next, we’ll bring everything together and show why trust-first referrals outperform spammy ones—and how they help you scale faster.

Read Trust-First Referral Growth

Or revisit foundational architecture patterns:
Don’t Touch That Data

Copy

Leave a Comment

Your email address will not be published. Required fields are marked *