Does shifting email volume between IPs affect deliverability and IP reputation across different mailbox providers?

Key findings

• Independent reputation: Mailbox providers (like Gmail, Outlook, Yahoo) generally maintain their own distinct IP reputation scores and do not directly share this data with competitors.
• Indirect impact: An IP's poor reputation at one provider might indirectly affect others if it leads to inclusion on a public blocklist (blacklist) or is flagged by shared spam filters. This is one of the ways your email can get blacklisted.
• Traffic quality is key: If email volume causing issues on one IP is shifted to a new, warmed IP, that new IP will likely inherit similar deliverability problems unless the underlying traffic quality is addressed. This highlights the importance of understanding email volume impact.
• Mailbox provider changes: Coincidental changes or updates by a specific mailbox provider (such as Microsoft's recent adjustments) can lead to deliverability shifts independently of a sender's volume strategy. More information about IP reputation can be found on Mailjet's blog.

Key considerations

• Monitor per provider: Actively monitor your IP and domain reputation separately for each major mailbox provider.
• Segment audiences: Consider segmenting your audience and sending from different IPs based on engagement levels or email type.
• Warm new IPs: Always properly warm any new IP addresses, even when shifting existing volume from another IP. This is crucial whether you're using shared or dedicated IPs.
• Identify root causes: When deliverability drops, investigate all possible causes, including changes in sending practices, list quality, and mailbox provider policy updates.

Key opinions

• Observed declines: Marketers frequently notice a decline in deliverability (e.g., to Hotmail) on an older IP after shifting a segment of traffic (e.g., Gmail consumers) to a new, warming IP.
• Volume shift impact: There's a common question among marketers about whether such a volume shift directly causes reduced performance on the original IP.
• Coincidental issues: Many marketers report experiencing issues with specific mailbox providers (like Microsoft SNDS) around the same time, suggesting broader, external changes rather than individual sending actions. This can sometimes involve rate limits or reputation problems.
• Cross-provider influence: A key concern for marketers is whether a poor reputation for an IP at one mailbox provider (e.g., Gmail) could influence its reputation at another (e.g., Hotmail).
• IP vs. domain: Marketers often discuss the relative importance of IP versus domain reputation in overall deliverability, as both impact sender score. You can learn more about domain reputation here.

Key considerations

• Targeted warming: When moving segments to a new IP, tailor the warming process to the specific mailbox providers you're sending to.
• Monitor changes: Be vigilant for industry-wide reports of deliverability shifts at major ISPs, as these can explain issues unrelated to your direct actions.
• Engagement data: Use engagement data to identify and isolate problematic segments of your audience, rather than simply shifting them to new IPs.
• Consistency: Strive for consistent sending patterns to each mailbox provider from a given IP to maintain a stable reputation.

Key opinions

• Direct sharing is rare: Experts generally agree that mailbox providers do not, as a rule, directly share IP reputation data with each other.
• Indirect correlation: An indirect link might exist if one receiver contributes to shared spam filters or blocklists that other receivers also utilize. This is a subtle yet important distinction.
• Traffic quality transfer: If the quality of the email traffic (e.g., high complaints or spam trap hits) causing poor deliverability on one IP is merely shifted to another IP, the new IP is likely to experience similar problems.
• Mailbox provider updates: Deliverability changes can often be attributed to ongoing updates or stricter filtering policies implemented by mailbox providers themselves, rather than internal volume shifts. This is especially true for major providers like Outlook, as noted by industry experts.
• Consistency and warming: Maintaining consistent sending volume and carefully warming new IPs are crucial for building and preserving a good reputation.

Key considerations

• Focus on content and list: Prioritize the quality of your email content and the cleanliness of your recipient lists, as these are primary drivers of reputation.
• Monitor blocklists: Regularly check common public blocklists (blacklists) to see if your IPs are listed, as this is a direct way deliverability can be impacted across providers. Suped provides a blocklist monitoring service.
• Diagnose carefully: Avoid jumping to conclusions about cross-provider reputation sharing. Instead, perform thorough diagnostics for each mailbox provider.
• Adapt to provider changes: Stay informed about deliverability policy updates and changes from major mailbox providers, as these can significantly alter outcomes. Review IP reputation categories for more.

Key findings

• IP reputation fundamental: IP reputation is consistently cited as a crucial factor directly affecting email deliverability and inbox placement. More info on email sender reputation.
• Dedicated vs. shared: Documentation often distinguishes between dedicated and shared IPs, noting that senders have more control over dedicated IP reputation, whereas shared IP reputation can be influenced by others.
• Volume fluctuations: Significant fluctuations in sending volume, particularly on new IPs or during peak periods, can negatively impact reputation and deliverability.
• Separate sending streams: Best practices often recommend using separate IP addresses for different types of email (e.g., transactional vs. marketing) to isolate their reputations. Learn more about IP vs. domain reputation.
• Impact of poor sending: Sending too much email too quickly on a new IP without proper warming can quickly tarnish its reputation.

Key considerations

• Strict warming schedules: Adhere to recommended IP warming schedules for new IPs, even when transferring established email streams.
• Audience segmentation: Segment your audience based on engagement to ensure high-quality traffic is sent from IPs critical to your deliverability.
• Consistent volume: Maintain consistent sending volumes to avoid sudden drops or spikes that can trigger spam filters.
• Domain and IP alignment: Ensure proper alignment between your sending domain and IP reputation for optimal inbox placement. Suped covers domain and IP reputation.