Summary
Synchronizing unsubscribes between two ESPs during a migration (or when operating in parallel) is a critical task for maintaining compliance and a healthy sender reputation. Failure to do so can lead to unwanted emails, increased spam complaints, and potential blocklisting. The primary challenge often lies in the capabilities of the older ESP, especially concerning custom unsubscribe links and real-time API access. Various strategies can be employed, ranging from manual bulk exports to sophisticated API integrations, depending on the tools available and the duration of the parallel sending phase.
Key findings
- Compliance risk: Hiding unsubscribe links is strongly discouraged and can lead to severe deliverability penalties and legal issues, as it violates anti-spam laws like CAN-SPAM and GDPR.
- API integration: The most robust and timely method for synchronization involves using APIs to pull unsubscribe data from one ESP and push it to the other. This requires both platforms to support adequate API functionalities.
- Master list concept: Maintaining a single 'master' unsubscribe list, often managed by the new ESP or an external CRM, simplifies the process of updating suppression records across all sending platforms. This also ties into how to manage bounced and spam complaint users.
- List-Unsubscribe header: A properly configured List-Unsubscribe header is crucial for modern email clients and should ideally point to a custom page or email address that can capture unsubscribe requests from all sources.
Key considerations
- Old ESP limitations: If the old ESP lacks custom unsubscribe link support or robust API access, consider workarounds like periodic manual exports or parsing unsubscribe notification emails, acknowledging these are less timely.
- Migration duration: The length of time you intend to use both ESPs in parallel will dictate the urgency and complexity of the synchronization method. Short overlap allows for simpler methods.
- Deliverability impact: Inaccurate or delayed unsubscribe synchronization can negatively impact sender reputation and lead to email blocklisting (or blacklisting). This is a common pitfall in ESP migration, as noted by Uplers in their blog on common migration pitfalls.
- Testing and validation: Thoroughly test any synchronization mechanism to ensure that unsubscribe requests are processed accurately and promptly across both platforms.
What email marketers say
Email marketers often face the practical challenges of ESP migration, particularly when immediate, real-time synchronization of unsubscribes isn't natively supported by older platforms. Their experiences highlight the need for creative, often multi-step, solutions to bridge the gap and maintain a positive subscriber experience during the transition period. The consensus leans heavily against deceptive practices like hiding unsubscribe links due to the severe negative consequences for deliverability.
Key opinions
- Direct syncing preferred: The ideal solution involves directly pulling unsubscribes from the old platform and applying them to the new one, often via backend APIs or batch uploads.
- Hidden links are risky: Hiding unsubscribe links is considered poor practice and could be flagged by spam filters, even if a broken List-Unsubscribe header might be a more immediate technical concern.
- Master list strategy: A robust approach involves maintaining a master subscriber list, regularly syncing it between ESPs, where unsubscribes on either platform update the master list.
- Batch syncing is viable: Scripted, batch synchronizations performed a few times daily are often sufficient for practical purposes, balancing timeliness with operational complexity.
- Manual alternatives: For platforms without advanced API capabilities, an email address as an unsubscribe option can serve as a low-tech fallback, though it's less efficient.
Key considerations
- Timeliness is key: Unsubscribe synchronization must be timely, especially if both platforms are sending simultaneously, to avoid re-mailing unsubscribed users.
- API capabilities: The success of automated synchronization largely depends on the new ESP's ability to trigger actions based on unsubscribes (callbacks) and the old ESP's API access for pulling data.
- Avoid workarounds: While hiding links might seem like a quick fix, it is detrimental to deliverability and is not a recommended long-term solution during an ESP migration and warmup.
- Long-term parallel operation: If using both platforms for a prolonged period, a robust, automated synchronization mechanism is essential to manage subscriber lists effectively and prevent issues. Consider the advice from Stripo.email on safe data transfers during migrations.
- Mitigating potential errors: Syncing via backend APIs or scheduled list uploads/downloads generally offers more control and is easier to troubleshoot if issues arise, minimizing the potential for errors.
Marketer view
Marketer from Email Geeks explains they encountered a problem while migrating between ESPs where they needed to synchronize unsubscribes. Their idea was to use a custom unsubscribe page sending API requests to both platforms. However, the old platform did not support custom unsubscribe links, meaning if the old link was removed, the default unsubscribe footer would be added. They expressed concern that hiding the old unsubscribe link in the template would be noticed by spam filters and should be avoided. They also noted that their List-Unsubscribe header appeared to be empty for their emails.
Marketer view
Marketer from Email Geeks suggests exploring the possibility of pulling unsubscribed users directly from the old platform and then applying those suppression records to the new platform. This approach would bypass the need for real-time synchronization via custom unsubscribe links if not supported by the legacy system.
What the experts say
Email deliverability experts consistently emphasize that unsubscribe management is a cornerstone of good sending practice. During ESP migrations, they advocate for proactive and robust strategies to ensure subscriber choices are respected across all platforms. Their advice typically centers on leveraging technology where possible, understanding the nuances of how mailbox providers handle unsubscribe requests, and maintaining strict compliance to protect sender reputation.
Key opinions
- Suppress globally: Unsubscribes should be suppressed globally across all sending platforms and lists, not just on the platform where the request was received. This prevents inadvertently re-mailing users from a different system.
- API integrations are best: Real-time or near-real-time synchronization via robust APIs is the most reliable method for managing suppression lists across multiple ESPs. This ensures rapid updates.
- Maintain one source of truth: Establish a single system, like a CRM or the primary new ESP, as the authoritative source for all subscriber statuses, including unsubscribes, to prevent data discrepancies.
- Monitor blocklists: Delays in processing unsubscribes can lead to higher complaint rates, which may result in your IP or domain being added to a blocklist (or blacklist). Proactive blocklist monitoring is essential.
- Compliance is paramount: Ensure all unsubscribe mechanisms comply with legal requirements like CAN-SPAM, GDPR, and CASL, regardless of the ESP being used.
Key considerations
- Phased migration strategy: For complex migrations, a phased approach allows for gradual list transfer and testing of unsubscribe synchronization, minimizing risk.
- Automate where possible: Manual processes for unsubscribe syncing are prone to error and delay. Automate as much as the ESPs allow.
- Handling re-subscribes: Have a clear policy for re-subscribes after list-unsubscribe, ensuring that previous unsubscribe requests are honored until a clear re-opt-in occurs.
- Consider sender reputation: Any misstep in unsubscribe management during migration can negatively impact your email domain reputation, leading to reduced inbox placement. Prioritize this to ensure seamless transition.
Expert view
Deliverability expert from SpamResource states that honoring unsubscribe requests is paramount for maintaining good standing with ISPs. Failing to suppress unsubscribed addresses across all sending systems, especially during a migration, will quickly lead to higher complaint rates and potential blocklisting, regardless of which ESP sent the email.
Expert view
Email deliverability consultant from Word to the Wise suggests that for migrations where two ESPs run in parallel, implementing a centralized suppression list (often in a CRM or a dedicated database) is the most effective approach. This ensures a single source of truth for all unsubscribe data that both ESPs can regularly query or update via API.
What the documentation says
Official documentation and email standards provide clear guidelines on managing unsubscribe requests. These resources underscore the importance of readily available unsubscribe mechanisms and prompt processing to ensure user privacy and maintain email ecosystem health. Compliance with these standards is fundamental for deliverability and avoiding penalties.
Key findings
- RFC 8058 (One-Click Unsubscribe): This RFC promotes a simplified, single-click unsubscribe method, typically implemented via the List-Unsubscribe header, which can significantly reduce complaints if properly managed across ESPs.
- Legal compliance: Regulations like CAN-SPAM (US), GDPR (EU), and CASL (Canada) mandate that unsubscribe mechanisms must be clear, conspicuous, and processed within specific timeframes. This applies regardless of how many ESPs are in use.
- Prompt processing: Mailbox providers and anti-spam organizations expect unsubscribe requests to be processed immediately, or at minimum within a few days. Delays increase spam complaints and blocklist risk.
- Sender reputation impact: Inaccurate or slow unsubscribe processing contributes negatively to sender reputation metrics tracked by ISPs, such as complaint rates, as highlighted by Klaviyo Help Center on ESP migration.
Key considerations
- API capabilities: Review the API documentation of both ESPs to understand their capabilities for exporting and importing suppression lists, or for triggering webhooks upon unsubscribe events.
- Data format consistency: Ensure that unsubscribe data (e.g., email addresses) can be exchanged in a consistent format between ESPs to facilitate accurate synchronization. Mailmodo support suggests importing subscribers and suppression lists as a key step.
- Fall-back mechanisms: Have a manual or semi-automated process for syncing unsubscribes in case API integrations fail or are unavailable for a period.
- Testing and auditing: Regularly test unsubscribe paths on both ESPs during the migration to confirm that all requests are captured and synchronized correctly.
Technical article
The RFC 2369, concerning the List-Unsubscribe header, specifies that senders should provide a method for recipients to easily unsubscribe. This typically involves a mailto: URI or an http: URI. During migration, ensuring both ESPs properly generate and respect this header is critical for deliverability, particularly for major mailbox providers.
Technical article
CAN-SPAM Act documentation states that commercial emails must include a clear and conspicuous way for recipients to opt out of future messages. This opt-out mechanism must be functional for at least 30 days after the email is sent, and requests must be honored within 10 business days. This legal requirement applies universally, regardless of sender's ESP infrastructure.
Related resources
10 resources
Related pages
What are the best practices for migrating to a new ESP while retaining sender reputation?
How to resolve email deliverability issues and IP blocks when migrating to a new ESP?
What are the best practices for managing unsubscriptions from multiple email lists?
How do mailbox providers handle re-subscribes after list-unsubscribe and how long does it take to process unsubscribe requests?
Should I clean my email list when migrating to a new ESP?
What are best practices for managing bounced, unsubscribed, and spam-complaint users in email marketing?
Should you continue sending emails from an old ESP during migration and warmup?
How your email address ends up on a blacklist
A simple guide to DMARC, SPF, and DKIM
