How long does IP warming usually take?

IP warming typically takes anywhere from 4 to 8 weeks, but it can vary based on your sending volume, list quality, and engagement rates. For higher volumes, it might take longer. Consistency and careful monitoring are more important than rigid timelines.

Is IP warming really necessary?

Yes, it is crucial. Sending a large volume of emails from a new or inactive IP without warming can trigger spam filters and lead to your emails being marked as spam or blocked. ISPs need to see a gradual, consistent sending pattern to build trust in your IP and domain.

Which subscribers should I send to first during IP warming?

Start with your most engaged subscribers first. These are recipients who have recently opened or clicked your emails. Sending to an active, responsive audience helps generate positive engagement signals, which are vital for building a good sender reputation during the warming process.

What should I do if I encounter deliverability issues during IP warming?

If you encounter issues during IP warming, such as high bounce rates or emails going to the spam folder, pause or reduce your sending volume immediately. Analyze your email content, list quality, and engagement metrics. If using a volume-based approach, consider switching to an ISP-based strategy to pinpoint the specific problematic provider.

Do I need to warm up a shared IP address?

While shared IPs typically have a pre-existing reputation, warming might still be necessary when migrating ESPs, especially if your sending volume is significant or your previous sender reputation was poor. This helps ensure a smooth transition and maintains consistent deliverability from the new shared IP.

What are the best practices for ISP-based vs volume-based IP warming strategies? - Sender reputation - Email deliverability - Knowledge base

Establishing a positive sender reputation is fundamental for successful email deliverability, especially when starting with a new or re-purposed IP address. This critical process, known as IP warming, involves gradually increasing your email sending volume over time, allowing Internet Service Providers (ISPs) to observe your sending habits and build trust in your mail.

The core debate in IP warming strategies often revolves around two primary approaches: ISP-based warming and volume-based warming. Both aim to achieve the same goal, but they differ significantly in their methodology and the level of granular control they offer. Understanding these distinctions is key to choosing the most effective strategy for your specific email program.

Volume-based IP warming: the general approach

Volume-based IP warming focuses on a steady increase in overall sending volume across your entire recipient list, regardless of their email provider. The idea is to ramp up your total email count daily or weekly, letting the distribution to various ISPs naturally follow your list composition. This method is often favored for its simplicity and reduced administrative overhead.

This approach assumes that major ISPs have sophisticated enough reputation systems to handle a general ramp-up, as long as engagement rates remain high and complaints stay low. It works well for senders with diverse, organically grown lists where no single ISP dominates the subscriber base excessively. The primary benefit is ease of management, as you don't need to segment your lists by domain for the warming process.

However, a purely volume-based strategy can sometimes mask issues with specific ISPs. If a particular provider is more sensitive to new sending patterns or has tighter filtering, a general volume increase might lead to blockages or inboxing issues at that specific ISP without immediate, clear indicators of where the problem lies. For more details on dedicated IP warm-up, refer to our guide on best practices for dedicated IP warm-up.

ISP-based IP warming: the granular approach

ISP-based IP warming involves segmenting your audience by email domain (e.g.,

Google,

Microsoft,

Yahoo) and then gradually increasing your sending volume to each specific ISP individually. This granular approach allows for precise control over your sending reputation at each major mailbox provider.

The primary advantage of ISP-based warming is the ability to monitor and react to specific ISP performance in real-time. If you encounter deliverability issues, you can pinpoint the exact provider causing the problem and adjust your sending volume or content strategy for that ISP without impacting others. This can lead to a faster and more controlled warm-up, especially for senders with a history of deliverability challenges or a high concentration of recipients at a few key ISPs. Learn more about specific strategies for warming email sending IPs by individual ISP in our detailed article.

However, this method requires more intensive micromanagement. It demands more complex segmentation, careful monitoring of multiple reputation metrics (like spam complaint rates, bounce rates, and engagement), and frequent adjustments to sending volumes per domain. This can be particularly challenging for B2B senders due to the fragmented nature of corporate domains.

ISP-based warming

Control: Offers granular control over sending volumes and reputation per individual ISP.
Issue identification: Allows for rapid identification and mitigation of issues at specific mailbox providers.
Speed: Can potentially lead to a faster overall warm-up, especially for high-volume senders.
Complexity: Requires more sophisticated segmentation and active management.
Applicability: Best for senders with clear ISP breakdowns or historical issues with specific providers.

Volume-based warming

Control: Simpler to manage, with a general ramp-up across all recipients.
Issue identification: Issues can be harder to attribute to a specific ISP, potentially delaying resolution.
Speed: May be slower if specific ISPs are particularly strict or if list quality varies widely.
Complexity: Lower overhead, less demanding in terms of daily adjustments.
Applicability: Suitable for senders with highly engaged, diverse lists and no prior deliverability flags.

Choosing the right strategy for your needs

The choice between ISP-based and volume-based IP warming often depends on several factors, including your historical sender reputation, the composition of your email list, and your team's available resources. For new IPs, gradually increasing your email send volume over several weeks is a universal best practice, as noted by Twilio SendGrid’s guide to IP warm up.

If you are migrating from an ESP or have faced prior deliverability issues (such as being on a blocklist or blacklist), an ISP-based approach can provide the detailed insights needed to resolve specific problems. This allows you to address particular ISP sensitivities directly. Conversely, if you have a clean slate, a highly engaged list, and limited resources for granular monitoring, a volume-based approach is often sufficient and more practical. The most effective approach for warming up an IP address for email sending often involves a strategic combination of these ideas, as highlighted in Adobe’s deliverability guide.

Regardless of the strategy chosen, consistent sending volume and careful monitoring are paramount. Avoiding sudden spikes in email volume and maintaining a consistent daily sending pattern helps build trust with ISPs. Regularly checking your email deliverability metrics, including open rates, click-through rates, and complaint rates, is crucial for both methods.

Important IP warming advice

When warming an IP, consistency is king. Sudden large email blasts from a new IP can quickly land you on a blocklist (or blacklist), significantly hindering your email deliverability. Always prioritize quality engagement over raw volume, especially in the early stages. Remember, the goal is to show ISPs that you are a legitimate sender sending desired mail.

For advice on how to fix issues during the warming process, see our guide on fixing an IP warming strategy with Gmail block.

Views from the trenches

Best practices

Maintain a consistent sending volume once warmed up to sustain your sender reputation.

Always start with your most engaged subscribers during the initial warming phase.

Segment your list to send to highly active users first, regardless of the warming strategy.

Utilize diverse content during warming to mimic natural sending patterns.

Ensure all authentication records (SPF, DKIM, DMARC) are correctly configured.

Common pitfalls

Sending too much too soon, leading to immediate blockages or high spam rates.

Failing to monitor deliverability metrics closely during the warm-up period.

Ignoring feedback loops from ISPs, missing critical reputation signals.

Trying to warm up with unengaged or old lists, which results in low engagement.

Not having a clear escalation plan if deliverability issues arise.

Expert tips

Consider a hybrid approach: start volume-based, then switch to ISP-based if issues arise.

Proactively communicate your warming schedule with major ISPs where possible.

Focus on the quality of your list and content over mere volume increases.

Don't warm up with time-sensitive emails, as the process can take weeks.

Monitor Cisco Talos Intelligence for insights into your sending health.

Expert view

Expert from Email Geeks says a granular ISP-based approach often yields great results, but volume-based warming works well due to improved provider reputation and inbound deliverability management technology.

2023-09-19 - Email Geeks

Expert view

Expert from Email Geeks says volume-based warm-ups are generally effective, but recommends specifically breaking out Microsoft (Outlook, Hotmail, Live) for separate attention due to their unique filtering.

2023-09-19 - Email Geeks

Finding your optimal warming path

Both ISP-based and volume-based IP warming strategies are valid paths to establishing and maintaining a strong sender reputation. The best approach for you will largely depend on your unique email sending profile, including the size and diversity of your list, your historical deliverability performance, and the resources you have available for monitoring and adjustment.

Ultimately, successful IP warming prioritizes sending quality content to engaged recipients, gradually increasing volume, and continuously monitoring performance. By adhering to these principles, you can build the trust necessary for consistent inbox placement and maximize your email program's effectiveness.