How many IPs are needed per million emails sent daily?
Matthew Whittaker
Co-founder & CTO, Suped
Published 3 May 2025
Updated 19 Aug 2025
6 min read
When trying to figure out how many IP addresses are needed to send a million emails daily, it is important to understand that there isn't a single, straightforward answer. The ideal number of IPs depends on a complex interplay of factors, including your sender reputation, the type of content you are sending, the engagement of your audience, and the specific policies of the receiving mailbox providers.
A common rule of thumb often cited in the industry suggests that one dedicated IP address can handle roughly two million emails per day. However, this is more of a general guideline for well-maintained sending programs with excellent reputations. If your sending practices are not optimal, or if you are just starting with a new IP, this volume might be significantly lower.
The goal is not simply to push out a large volume of mail, but to ensure that mail reaches the inbox effectively and consistently. This means focusing on deliverability and maintaining a strong sender reputation above all else. Adding more IP addresses without addressing underlying deliverability issues can sometimes create more problems than it solves.
Factors influencing IP needs
Several critical factors influence how many emails an IP address can successfully deliver each day without encountering throttling or blocklisting (or blacklisting). Understanding these factors is key to optimizing your IP strategy.
Sender reputation: This is paramount. A positive reputation, built through consistent sending of wanted mail, low complaint rates, and low bounce rates, allows you to send higher volumes. Mailbox providers, like Google, prioritize mail from trusted senders, granting them more resources and faster delivery. For more on this, check out our guide on understanding your email domain reputation.
Email content quality: Spammy content, excessive links, or poor formatting can trigger filters, regardless of IP volume.
Audience engagement: High open and click-through rates signal to ISPs that your emails are valued, contributing positively to your reputation.
List hygiene: Regularly cleaning your email list to remove invalid or inactive addresses helps avoid bounces and spam traps, which can quickly damage your IP's standing.
Mailbox providers often have their own internal rate limits or throttling mechanisms that dictate how much email they will accept from a single IP address within a given timeframe. These limits are dynamic and based on your sending history and reputation. For instance, some providers might initially accept a lower volume, then gradually increase it as your reputation improves.
Typical volume guidelines and considerations
While there is no universally fixed number, industry experience provides some helpful benchmarks. Many email service providers (ESPs) and deliverability experts suggest that a single, well-warmed dedicated IP can generally support between one to two million emails per day. However, some high-volume senders with exceptional reputations report sending even more, sometimes up to four million messages daily from one IP.
Shared IP addresses
Good for lower volumes, generally under 100,000-250,000 emails per month. Reputation is influenced by other senders using the same IP pool.
Volume: Typically for lower senders. Salesforce Marketing Cloud recommends dedicated IPs for over 100,000 emails per month.
Reputation control: Shared among multiple users, so reputation can be affected by others' sending practices.
Warming: Generally managed by the ESP.
Dedicated IP addresses
Ideal for high-volume senders, typically those sending 250,000+ emails per month. You are solely responsible for managing its reputation. Warming an IP is crucial.
Volume: Suitable for millions of emails daily. SendGrid suggests one dedicated IP for every three to four million messages sent daily, while SparkPost recommends 2 to 5 million per day from a single IP after proper warmup.
Reputation control: Your sending practices solely determine your IP's reputation, allowing for greater control.
Warming: Requires a systematic IP warming process to build trust with ISPs.
IP warming is a critical component of establishing and maintaining good deliverability, particularly for dedicated IP addresses. It involves gradually increasing your sending volume over time to build a positive reputation with mailbox providers. Without proper warming, even a single IP address will struggle to deliver 100,000 emails per day, let alone a million.
The impact of ISP throttling and blocklists
Mailbox providers actively manage incoming email traffic to protect their users and ensure stable service. They have sophisticated systems that monitor IP addresses and domains. If they detect unusual sending patterns, high complaint rates, or other signs of questionable activity, they will respond by throttling your email, delaying delivery, or outright blocking your messages.
Throttling limits the number of connections or emails accepted from an IP address, essentially slowing down your sending. This often occurs when an IP is new, has a questionable reputation, or is attempting to send too much volume too quickly without a history of good sending. You might notice this as delays in your delivery logs or error messages indicating temporary deferrals. Some ISPs, like Comcast, are known to impose such limits based on source IP.
Being placed on an email blocklist (or blacklist) is a more severe consequence of poor sending practices. When your IP is blocklisted, many mailbox providers will simply reject all emails coming from that IP, preventing them from reaching the inbox. This can severely impact your ability to send a million emails daily, as a significant portion of your mail may not be accepted. You can learn more about this in our article, What happens when your IP gets blocklisted.
Strategic management of IP addresses
For senders aiming for high volumes like a million emails per day, managing your IP addresses strategically is far more effective than simply adding more. The underlying issues that cause throttling or blocklisting, such as poor list quality or low engagement, must be addressed first.
Proactive strategies
Maintain pristine lists: Regularly clean your email lists to remove bounces, unsubscribes, and unengaged contacts.
Segment audiences: Send targeted, relevant content to different segments to boost engagement.
When encountering throttling from mailbox providers, implementing a backoff mode on your Mail Transfer Agent (MTA) is crucial. This mechanism instructs your sending system to temporarily slow down or pause sending to a specific domain or IP if it receives deferral messages, preventing further damage to your reputation. This proactive approach helps build trust and improve long-term deliverability.
Example: SMTP header indicating a delivery delayplain
Received: from mail.example.com (mail.example.com [192.0.2.1])
by mx.google.com with ESMTPS id abcdefg.hijklmno.pqrstuv.wxyz
for <recipient@gmail.com>;
Mon, 1 Jan 2024 10:00:00 -0800 (PST)
// ... later in the header from Gmail ...
X-Google-Smtp-Response-Time-Seconds: 4500
An apparent delay in email delivery, as seen in some SMTP headers, might indicate that the Mailbox Provider (MP) accepted the message but delayed its delivery to the recipient's inbox due to reputation concerns, a situation that often implies throttling. Alternatively, the delay might have occurred even before the MP received the email, meaning the sending ESP or MTA experienced a bottleneck, or was itself experiencing issues pushing the email out at the desired rate.
Views from the trenches
Best practices
Maintain a consistent sending volume to keep your IPs warm and build a stable reputation with mailbox providers.
Prioritize list hygiene and regularly remove unengaged subscribers, hard bounces, and any known spam trap addresses.
Implement feedback loops and promptly address user complaints to signal good sending practices to ISPs.
Monitor your sender reputation metrics (spam complaints, bounce rates) using tools like Google Postmaster Tools.
Invest in robust email authentication protocols such as SPF, DKIM, and DMARC to build trust and prevent spoofing.
Common pitfalls
Rapidly increasing sending volume on a new IP without proper warming, leading to throttling or blocklisting (blacklisting).
Failing to monitor deliverability metrics, missing early signs of reputation decline or delivery issues.
Acquiring email lists or sending to unconfirmed opt-in contacts, which increases spam complaint rates.
Ignoring soft bounces and temporary deferrals, which can accumulate and signal issues to mailbox providers.
Using generic or poorly formatted email content that triggers spam filters and negatively impacts engagement.
Expert tips
Consider a phased approach for new IPs, starting with small, highly engaged segments before increasing volume.
Utilize subdomains for different types of email (transactional, marketing) to isolate reputation risks.
Ensure your sending infrastructure is configured for adaptive sending rates and backoff mechanisms to respond to ISP signals.
Actively engage with your audience to encourage opens, clicks, and replies, which positively influence your reputation.
Regularly review your email headers for delivery delays or explicit throttling messages from mailbox providers.
Marketer view
Marketer from Email Geeks says one IP can handle up to 2 million sends in a day, based on sender-side limits from platforms like Salesforce Marketing Cloud.
2019-08-02 - Email Geeks
Expert view
Expert from Email Geeks says there isn't a hard limit, but 2 million sends per day per IP is a practical benchmark, with some high-quality senders exceeding 4 million.
2019-08-02 - Email Geeks
The dynamic nature of IP capacity
Ultimately, the number of IP addresses required to send a million emails daily is not a static figure. It is a dynamic target influenced by the quality of your sending program and the trust you have built with mailbox providers. While a single IP can often handle this volume for well-regarded senders, prioritizing sender reputation, consistent warming, and proactive deliverability management will always be more effective than simply adding more IPs.
Comcast, are known to impose such limits based on source IP.
