How long does it take to warm up an IP address for sending 25 million emails per day?

Key findings

• Extended duration: Warming up to 25 million emails per day on a single IP could theoretically take 150 to 190 days (5 to 6 months), assuming exceptionally high recipient engagement. This is far beyond the typical 4-8 weeks often cited for more common sending volumes. Standard IP warming schedules are designed for much lower initial volumes and gradual increases.
• Engagement is paramount: The success of IP warming is less about raw volume and more about the engagement ratio. A low engagement rate (e.g., 20% opens) for 25 million emails means Mailbox Providers process a massive number of unread or unwanted messages, negatively impacting your reputation.
• Single IP limitations: A single IP address is often insufficient and creates a significant bottleneck for sending 25 million emails daily. Many ISPs (Internet Service Providers) have limits on the rate at which they accept emails from a single IP, regardless of its reputation. For more on scaling, consider how many IPs are needed.
• List quality and destinations: The quality of your email list and the diversity of the Mailbox Providers it targets play a crucial role. A poor list or one heavily concentrated on a single MBP can prolong the warm-up and lead to blocklisting. Maintaining a high-quality list is essential for email deliverability issues.

Key considerations

• Multiple IPs: For volumes of 25 million emails per day, a portfolio of dedicated IP addresses is almost certainly required to distribute sending load and mitigate risk. This aligns with common practices for high-volume senders.
• Gradual ramp-up: Regardless of the number of IPs, a slow and steady increase in volume, starting with your most engaged subscribers, is critical. This allows ISPs to build trust in your sending patterns and reputation. Maileroo Blog suggests aiming for at least 30 days of email sending history. You can find more details in this IP warm-up guide.
• Engagement strategy: Prioritize sending to highly engaged segments first during warm-up. This helps demonstrate positive sending behavior to ISPs. A low engagement rate will lead to emails going to the spam folder, a critical topic discussed in why your emails are going to spam.
• Monitoring and adaptation: Vigilant monitoring of deliverability metrics (opens, clicks, bounces, complaints, blocklist appearances) is essential. Be prepared to adjust your sending volume and strategy based on real-time feedback from ISPs and postmaster tools. Monitoring your Google Postmaster Tools Domain Reputation is a crucial part of this process.
• Risk mitigation: Ignoring proper warm-up can lead to severe consequences, including emails being sent directly to spam folders, temporary throttling, or permanent blocklisting of your IP and domain. This could stall your email program for months.

Key opinions

• Volume vs. IP capacity: Many marketers express concern that 25 million emails a day is an excessive volume for a single dedicated IP, highlighting it as a significant bottleneck. This sentiment is often echoed when discussing maximum daily email volume.
• Consequences of insufficient warm-up: Marketers frequently point out the severe ramifications of not warming up properly, including emails hitting spam folders or getting blocked, which can cripple a campaign. This is a common challenge for those facing large sends without sufficient IP warmup.
• Engagement over volume: The focus should shift from just the number of emails to how engaged the recipients are. A high volume with low engagement is seen as a major red flag for ISPs, as Maileroo Blog explains. For improving engagement, consider strategies outlined in how to increase email click through rate.
• Redundancy needs: There's a strong consensus that relying on a single IP for such a massive volume lacks reasonable redundancy, making the system prone to failure, regardless of warm-up. This suggests a multi-IP approach is essential.

Key considerations

• Max emails per IP: Understanding the realistic maximum email volume per IP per day is a critical question for marketers to prevent deliverability issues.
• ISP processing capacity: It's important to recognize that some ISPs simply cannot accept emails fast enough from a single IP, regardless of its reputation, making high single-IP volumes challenging. More information about how ISPs handle high volume sends can be found in this Twilio SendGrid email guide.
• Audience segmentation: Segmenting audiences and sending to different Mailbox Providers (MBPs) across multiple IPs can help distribute the load and manage reputation more effectively. This is a key aspect of IP warmup strategy.

Key opinions

• Volume vs. engagement balance: The primary factor is not just the volume itself, but the relationship between volume and user engagement. High volume with low engagement (e.g., 20% read rate for 25M emails resulting in 20M unread messages) burdens ISPs and leads to poor reputation. Experts emphasize understanding why your email deliverability rate is wrong.
• Single IP inadequacy: Sending 25 million emails per day through a single IP is generally considered unsustainable and creates a significant bottleneck. This setup is highly prone to failure regardless of other positive factors due to ISP volume limits and redundancy issues.
• Theoretical vs. practical warm-up: While academically a single IP might take 150-190 days to warm up to 25M emails daily under ideal engagement conditions, experts stress this is largely theoretical and not a practical real-world scenario.
• Destination diversity: The number of Mailbox Provider destinations matters. Sending 25 million emails to a single MBP will take much longer and be harder than distributing that volume across many different MBPs. This also impacts how to warm up new IP addresses.

Key considerations

• Infrastructure questions: Before deep diving into IP/domain warm-up schedules for such large volumes, foundational questions about existing infrastructure, sending history, and list acquisition methods should be addressed. Effective email deliverability testing can help identify early issues.
• ISP acceptance rates: Recognize that some ISPs may not accept emails fast enough from a single IP address, regardless of its established reputation. This necessitates a diversified IP strategy. More about how different ISPs behave can be found on Word to the Wise.
• Focus on deliverability best practices: Beyond warming, sustained good deliverability for high volumes requires adherence to best practices, including proper authentication (SPF, DKIM, DMARC), list hygiene, and content quality. These factors are crucial to boost email deliverability rates.

Key findings

• Gradual volume increase: Documentation emphasizes the importance of gradually increasing email volume from a new or dormant IP. This helps establish trust with Mailbox Providers and builds a positive sender reputation. A common recommendation is to build at least 30 days of email sending history, as stated by the Maileroo Blog's IP warm up guide.
• Typical timelines: While 25 million emails is an outlier, general IP warming guidelines suggest a period of 4 to 8 weeks on average. Twilio's Email Guide to IP Warm Up outlines how proper warm-up can allow sending millions per day. However, this is for a fully established, well-reputed IP, not the warm-up phase itself for such a high target.
• Engagement metrics: Successful warming relies heavily on sending to engaged users. Documentation frequently highlights the impact of opens, clicks, and low complaint rates on building reputation. High complaint rates or spam trap hits during this phase can derail progress, emphasizing the need for robust blocklist monitoring.
• Domain vs. IP warming: Some documentation differentiates between IP and domain warming, noting that domain warming can often take longer (e.g., 2-3 months), as highlighted by the DeBounce blog. Both are critical for overall sender reputation.

Key considerations

• Sender reputation building: The core purpose of IP warming is to establish a positive sender reputation with Mailbox Providers. This involves demonstrating consistent, legitimate sending behavior over time.
• ISP-specific requirements: While general guidelines exist, individual ISPs may have unique thresholds or unstated limits on initial volumes and ramp-up rates. Understanding and adapting to these implicit rules is crucial. For example, Outlook's new sender requirements highlight specific compliance needs.
• Impact of poor warm-up: Documentation consistently warns that skipping or rushing IP warm-up leads to emails being flagged as spam, deferred, or outright rejected, which can quickly land your IP on a blacklist or blocklist.