How does sending monthly newsletters to a large list impact dedicated IP reputation?
Matthew Whittaker
Co-founder & CTO, Suped
Published 21 Jun 2025
Updated 15 Aug 2025
6 min read
When managing email deliverability, the choice between a shared and a dedicated IP address is a crucial one. While a dedicated IP offers the distinct advantage of controlling your own sending reputation, it also comes with increased responsibility. This is especially true for senders who dispatch large volumes of emails infrequently, such as monthly newsletters to a list of over a million subscribers.
My experience has shown that consistent sending volume is paramount for maintaining a healthy dedicated IP reputation. A large, bursty send once a month can pose significant challenges that might lead to unexpected deliverability issues, including emails landing in spam folders or even getting blocklisted (or blacklisted). Let's explore why this happens and what strategies can mitigate the risks.
The challenge of inconsistent volume
Mailbox providers, like Gmail and Outlook, rely heavily on consistent sending patterns to establish and maintain a positive sender reputation for an IP address. This consistency helps them distinguish legitimate senders from potential spammers. When you send 1.3 million emails in a single day once a month, followed by weeks of inactivity, it creates a highly inconsistent volume profile.
This bursty sending can negatively impact your dedicated IP reputation. Mailbox providers' algorithms are designed to detect unusual spikes or drops in volume, which can be interpreted as suspicious activity. Such behavior can trigger spam filters or even lead to your IP address being temporarily throttled, preventing your emails from reaching the inbox.
Maintaining a dedicated IP's reputation requires ongoing, regular sending. Think of it like a muscle, it needs to be exercised consistently to stay strong. A sudden, large workload after a period of rest can lead to poor performance. For more on maintaining this, consider how to maintain dedicated IP reputation with ISPs.
Why mailbox providers care
The reason mailbox providers react this way is rooted in their efforts to combat spam. A sudden influx of emails from an IP that is usually quiet can resemble patterns often seen with spammers who acquire large lists and send them all at once. Even if your list is legitimate, the sending pattern itself can raise red flags.
Additionally, some internet service providers (ISPs) measure inactive days and factor that zero volume into an aggregate daily volume. This means that a large burst of emails on a single day, when averaged over a month including many zero-volume days, can appear as an unusually high daily deviation. This bursty sending behavior can lead to throttling or outright blocklists (blacklists).
An IP address (or even your domain reputation) being added to a blocklist can severely impact your deliverability. If your IP gets blocklisted, your emails may be rejected outright, preventing them from ever reaching your subscribers. It's vital to avoid this scenario, as recovering from a blocklist can be a lengthy process.
Strategies for managing reputation
For monthly newsletters to a large list, several strategies can help manage your dedicated IP reputation. One effective approach is to avoid sending the entire volume in a single burst. Instead, consider spreading the sends over a few days or even a week, if the content isn't time-sensitive.
Implementing a throttling method to dispatch the newsletter gradually can smooth out your sending volume. You can prioritize sending to your most engaged subscribers first, then progressively send to less engaged segments throughout the month. This helps establish a positive interaction history with mailbox providers early in your sending cycle.
Alternatively, if consistent daily or weekly sends are not feasible, you might consider if a dedicated IP is the right fit at all. For lower frequency sends, a shared IP pool might be more suitable, as the ESP (Email Service Provider) manages the overall reputation of the pool, balancing the sending patterns of multiple users. Here’s a comparison:
Dedicated IP for monthly sends
Control: You have full responsibility for your IP's reputation, for better or worse.
Volume consistency: Inconsistent large monthly sends can lead to throttling and blocklists.
Control: ESP manages the IP reputation across multiple senders.
Volume consistency: Good for irregular or low-volume sends as other senders contribute to consistency.
Warming: Often less intensive, as the pool is pre-warmed.
Best practices for success
Regardless of your IP choice, fundamental email sending best practices are critical. Your email list quality and the engagement levels of your recipients play a massive role. Even with perfect sending frequency, if your recipients aren't engaging, your reputation will suffer. Ensure your list consists of genuinely opted-in subscribers who consistently open and click your emails.
Regular list hygiene is essential. Remove inactive subscribers who haven't opened emails in a long time, as sending to unengaged contacts can harm your reputation and increase the likelihood of hitting spam traps. Regularly cleaning your list helps maintain a high engagement rate for your active subscribers, which signals positive behavior to mailbox providers.
Proper email authentication, including SPF, DKIM, and DMARC, is non-negotiable for any sender, especially those with a dedicated IP. These protocols verify your sender identity, making your emails appear more trustworthy to mailbox providers and reducing the chances of them being flagged as spam. Without them, even the most engaged list won't help.
Essential sending configurations for high deliverability
Implement DMARC: Ensure your DMARC policy is correctly configured to monitor and enforce email authentication.
Monitor your IP reputation: Regularly check blocklists (and blacklists) and leverage tools like Google Postmaster Tools to identify issues.
Maintain list hygiene: Remove unengaged subscribers and bounced addresses promptly to reduce spam complaints.
Views from the trenches
Best practices
Maintain a consistent sending volume, even if it means segmenting a large list and sending it over several days.
Prioritize highly engaged segments of your list to build positive reputation signals with mailbox providers.
Regularly clean your email list by removing unengaged subscribers and bounces to improve overall list quality.
Ensure all email authentication protocols like SPF, DKIM, and DMARC are correctly implemented and monitored.
Common pitfalls
Sending large volumes infrequently (e.g., once a month) can trigger spam filters due to inconsistent patterns.
Ignoring inactive subscribers leads to lower engagement rates, negatively impacting IP reputation.
Not warming up a new dedicated IP address gradually can cause immediate deliverability issues and blocklisting.
Failing to monitor IP reputation can result in unnoticed blocklistings and significant email delivery failures.
Expert tips
If monthly sends are unavoidable, consider spreading the send over 2-3 days using throttling to smooth the volume.
Highly engaged recipients are key, as their positive interactions can offset the challenges of irregular sending.
For very low frequency, high volume sends, a shared IP pool may offer more stability than a dedicated IP.
Always be prepared to be patient with IP warming; it takes time to build a strong reputation.
Marketer view
Marketer from Email Geeks says that sending monthly newsletters with 1.3 million contacts is problematic for a dedicated IP. Segmenting the list and sending to smaller groups more frequently can help maintain consistent volume history.
2020-06-30 - Email Geeks
Marketer view
Marketer from Email Geeks says that infrequent sending to large lists can cause issues because ISPs measure inactive days. The 'bursty' nature of sends can look like unusual behavior, leading to throttling or blocks.
2020-06-30 - Email Geeks
Navigating dedicated IP reputation
Sending monthly newsletters to a large list on a dedicated IP presents a unique set of challenges. While a dedicated IP offers control, its reputation is highly sensitive to consistent sending patterns.
For monthly sends of over a million emails, a dedicated IP might seem appealing for control, but the infrequent, bursty nature of the sends can actively harm your reputation by appearing suspicious to mailbox providers. This can lead to throttling, blocklisting, and ultimately, poor inbox placement. While it's possible to make it work with a highly engaged audience and meticulous adherence to all other email best practices, it requires a significant amount of effort and patience.
Consider carefully if a dedicated IP aligns with your sending frequency. For many, a well-managed shared IP pool might offer more reliable deliverability for infrequent, large-volume newsletters without the constant battle against inconsistent sending patterns. The key is to choose an IP strategy that complements your sending habits and allows you to maintain a consistently positive sender reputation.
