Summary
Resolving email deliverability issues and IP blocks when migrating to a new Email Service Provider (ESP) hinges on a multi-faceted approach. A fundamental step is the systematic IP warm-up, where sending volume is gradually increased to build a new sender reputation with Internet Service Providers (ISPs). This must be coupled with rigorous list hygiene, including removing unengaged and invalid contacts prior to migration, and segmenting your audience to send to the most engaged subscribers first during the warm-up period. Correctly configuring email authentication protocols, such as SPF, DKIM, and DMARC, on the new domain is also non-negotiable for establishing trust. Furthermore, proactive monitoring of deliverability metrics and understanding the nuances of shared IP blocks versus new sender status are vital for immediate issue resolution and sustained email success.
Key findings
- IP Warm-up is Essential: A systematic IP warm-up strategy is paramount when migrating to a new ESP or using new IPs. This involves gradually increasing sending volume to engaged subscribers over several weeks, allowing ISPs to establish trust and build a positive sender reputation, thereby preventing immediate IP blocks.
- Prioritize List Hygiene: Thoroughly clean your email list before migration by removing unengaged subscribers, invalid emails, and known complainers. This pre-migration scrubbing prevents high bounce rates and spam complaints that can immediately damage the new IP's reputation and lead to deliverability issues.
- Segment and Engage First: Segment your audience and send to your most engaged subscribers first during the IP warm-up phase. This approach helps build a strong initial reputation with ISPs, as positive engagement metrics are critical for consistent inbox placement and avoiding flags.
- Monitor Reputation Metrics: Continuously monitor reputation metrics like bounce and complaint rates closely, adjusting sending volume as needed to stay within good thresholds. Consistent sending volume and low complaint rates are crucial for maintaining good deliverability and avoiding blocks.
- Migrate Suppression Lists: It is critical to properly migrate all suppression lists, including bounces and unsubscribes, to the new ESP. Failing to do so can lead to sending to unengaged or invalid addresses, harming your new IP's reputation.
Key considerations
- Investigate Blocks: Before blindly resending blocked emails, especially from a new ESP, investigate the root cause of the block. For shared IP blocks, your ESP should ideally address underlying issues, as Microsoft often blocks for reasons beyond just a new sender.
- Understand Snowshoe Risk: Be aware that sending identical content from multiple, unrelated sources risks triggering snowshoe detection, a crucial consideration when using multiple ESPs for the same mail stream.
- Proper Authentication: Crucially, ensure all email authentication protocols-SPF, DKIM, and DMARC-are correctly set up and verified on the new ESP's domain. Proper DNS records signal legitimacy to ISPs, building trust and improving inbox placement, thereby reducing the likelihood of emails being flagged as spam or IP blocks.
- Comprehensive Monitoring: During and after migration, proactively monitor email deliverability, including inbox placement across major ISPs, spam folder placement, and bounce rates. This allows for immediate detection of IP blocks or reputation dips, enabling quick adjustments to sending strategy or technical configurations.
- ESP's Role in IP Blocks: Understand that if you are on a shared IP, your ESP is often responsible for resolving IP blocks, as these are typically due to abusive senders on the network rather than simply being a new sender, though being a fresh sender can influence filtering decisions.
What email marketers say
12 marketer opinions
Building on the foundation of strategic IP warm-up and rigorous list hygiene, a successful ESP migration also demands meticulous preparation and ongoing vigilance. It's crucial to understand the nuances of IP reputation, especially for shared pools, and to proactively address any deliverability challenges. Testing all campaign elements and integrations before full deployment, combined with comprehensive monitoring of key metrics, ensures a smooth transition and sustained inbox placement, avoiding the pitfalls of IP blocks or spam flagging.
Key opinions
- IP Warm-up is Essential: A structured warm-up process for new IPs or domains is fundamental, gradually increasing sending volume to build a trusted reputation with ISPs over several weeks and prevent immediate blocks.
- Prioritize List Hygiene: Pre-migration list cleaning, removing unengaged, inactive, or invalid contacts, is critical to avoid high bounce rates and spam complaints that could harm your new IP's standing and prevent deliverability issues.
- Segment and Engage First: When warming up, prioritize sending to your most engaged subscribers first, as their positive interactions contribute significantly to establishing a strong sender reputation and improving inbox placement.
- Monitor Deliverability Metrics: Continuously track key metrics like inbox placement, spam folder rates, and bounce rates across major ISPs to proactively detect and respond to any issues or reputation dips, enabling quick adjustments.
- Migrate Suppression Lists: Ensure all unsubscribe and bounce lists are accurately migrated to the new ESP to prevent sending to opt-outs or problematic addresses, which is vital for maintaining a healthy sending reputation and avoiding future issues.
Key considerations
- Investigate Block Reasons: Avoid blindly resending blocked emails; instead, first ascertain the root cause of the block, especially for shared IP blocks where the ESP's intervention may be necessary and they should be contacted.
- Understand Snowshoe Risk: Be mindful that sending identical content from multiple, unrelated sources or multiple ESPs for the same mail stream can trigger snowshoe detection, impacting deliverability.
- Verify Authentication Protocols: Thoroughly set up and verify all email authentication records-SPF, DKIM, and DMARC-on the new domain to signal legitimacy to ISPs and enhance inbox placement, reducing the likelihood of emails being flagged as spam or IP blocks.
- Thorough Platform Testing: Before a full migration, conduct comprehensive testing of all email campaigns, templates, and integrations on the new ESP to identify and resolve any technical issues that could impede deliverability.
- ESP's Role in Shared IPs: Recognize that for shared IP blocks, the ESP is typically responsible for resolution, as blocks often stem from issues with other senders in the pool rather than simply being a new sender, though newness can influence filtering.
Marketer view
Email marketer from Email Geeks explains that blindly resending blocked emails is never a good idea, especially from a different ESP, as it can appear spammy. He advises finding out why messages were blocked first and, for shared IP blocks, suggests contacting the ESP and ensuring proper DKIM signing and whitelabeled return paths.
26 Jun 2021 - Email Geeks
Marketer view
Email marketer from Email Geeks shares that sending the same content from multiple unrelated sources risks triggering snowshoe detection automation, which is important to consider when using multiple ESPs for the same mail stream.
8 Mar 2022 - Email Geeks
What the experts say
2 expert opinions
When transitioning to a new Email Service Provider (ESP), resolving potential email deliverability issues and IP blocks largely depends on establishing a solid sending reputation for new IP addresses. The foundational strategy for this is a meticulous IP warm-up, where email volume is increased incrementally. This controlled approach is vital because Internet Service Providers (ISPs) are inherently cautious of sudden, high-volume sending from unfamiliar IPs. A gradual warm-up allows ISPs to observe and assess the quality and engagement of the emails, thereby building the necessary trust that prevents immediate flagging, spam filter triggers, and subsequent IP blocks, ensuring emails reach their intended inboxes.
Key opinions
- Warm-up Prevents Immediate Blocks: Proper IP warm-up is crucial for new IPs, as skipping this gradual volume increase can immediately trigger spam filters and lead to IP blocks, making inbox delivery impossible.
- Gradual Volume Builds Trust: A gradual increase in sending volume allows Internet Service Providers (ISPs) to monitor email quality and establish trust with the new IP, resolving potential deliverability issues.
- ISPs Assess Sender Quality: The warm-up process enables ISPs to assess the sender's reputation and legitimacy, preventing their inherent wariness of high volume from unknown IP addresses.
Key considerations
- Avoid Skipping Warm-up: Failing to warm up new IP addresses when migrating to an ESP is a critical error that will almost certainly result in deliverability issues and IP blocks.
- ISPs' Caution with New IPs: Internet Service Providers are naturally cautious of sudden, high-volume sending from unknown IP addresses, necessitating a controlled ramp-up to prove sender legitimacy.
- Reputation Establishment Process: IP warm-up is not merely a technical step, but a reputation-building process vital for establishing trust and proving sender quality to ISPs over time.
Expert view
Expert from Spam Resource explains that IP warmup is crucial for establishing a good sending reputation when using new IP addresses, which is common when migrating to a new ESP. Failing to warm up IPs can lead to deliverability issues and IP blocks because ISPs are wary of high volume from unknown IPs. A gradual increase in sending volume allows ISPs to monitor email quality and build trust, thereby resolving potential problems.
16 Aug 2022 - Spam Resource
Expert view
Expert from Word to the Wise explains that IP address warmup is absolutely essential when migrating to a new ESP and beginning to send from new IPs. This process involves gradually increasing email volume over time, allowing ISPs to establish trust and assess the sender's reputation. Skipping warmup can immediately trigger spam filters and lead to IP blocks, making it impossible to reach the inbox. They emphasize that this controlled ramp-up prevents deliverability issues by proving you are a legitimate sender.
13 Nov 2021 - Word to the Wise
What the documentation says
5 technical articles
Resolving email deliverability issues and preventing IP blocks during an ESP migration critically depends on a methodical IP warm-up. This process involves a controlled, incremental increase in sending volume from new dedicated IP addresses, starting with small batches and gradually scaling up. Alongside this, continuous monitoring of crucial reputation metrics-such as bounce and complaint rates-is essential. Senders must be prepared to dynamically adjust their sending pace and volume based on these indicators to maintain a positive standing with Internet Service Providers. Maintaining consistent sending volume and prioritizing engaged recipients also play a vital role in building and sustaining trust, thereby ensuring consistent inbox placement.
Key findings
- Gradual IP Warm-up: Initiate sending from new IPs with low volumes and progressively increase sending rates over time to build a positive sender reputation with Internet Service Providers (ISPs), preventing immediate flags and blocks.
- Monitor Reputation Metrics: Rigorously monitor key reputation metrics like bounce and complaint rates, and sender scores (e.g., via Google Postmaster Tools), adjusting sending volume as needed to stay within healthy thresholds.
- Maintain Consistent Volume: Avoid sudden spikes in sending volume from new or unestablished IPs; instead, maintain a consistent sending pace to signal legitimacy and avoid triggering spam filters.
- Prioritize Engaged Recipients: During the warm-up phase, prioritize sending to highly engaged subscribers to generate positive interactions, which are crucial for establishing trust and improving deliverability.
- Adjust Sending Pace: Be prepared to adjust your sending pace and volume in real-time based on observed reputation metrics to prevent blacklisting and ensure consistent inbox placement.
Key considerations
- Deliberate Warm-up Schedule: Adhering to a deliberate, structured IP warm-up schedule-as advised by major ESPs-is non-negotiable for successfully migrating and avoiding deliverability penalties.
- ISP Trust Building: The primary goal of warm-up is to systematically build trust with ISPs, demonstrating consistent and positive sending behavior before attempting full volume.
- Real-time Metric Adjustment: The need for real-time monitoring of metrics and the flexibility to adjust sending volumes accordingly underscores that warm-up is an active, ongoing process, not a one-time setup.
- Avoiding Volume Spikes: A critical aspect is avoiding any sudden, large increases in email volume from new or warming IPs, as these are strong indicators of potential spam to ISPs and will lead to blocks.
- ESPs Emphasize Warm-up: The consistent emphasis on methodical IP warm-up across various ESPs and email deliverability guides highlights its universal importance as a best practice.
Technical article
Documentation from AWS Documentation advises users to follow a deliberate IP warm-up schedule when moving to a new dedicated IP, starting with low volumes of emails and gradually increasing sending rates. They stress the importance of monitoring reputation metrics like bounce and complaint rates closely and adjusting sending volume to stay within good thresholds to prevent IP blocks and ensure high deliverability.
12 Apr 2024 - AWS Documentation
Technical article
Documentation from Google's Bulk Sender Guidelines implicitly addresses migration by stating that high volume senders should ensure consistent sending volume and monitor their sender reputation within Postmaster Tools. They advise against sudden spikes in sending volume from new or unestablished IPs and emphasize the importance of low spam complaint rates and active engagement to maintain good deliverability and avoid being flagged.
10 Aug 2021 - Google's Bulk Sender Guidelines
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