Which IP type is best for infrequent, very high-volume email sends?

For truly inconsistent, high-volume sends (e.g., millions once every few months), shared IPs are generally better. Dedicated IPs require consistent sending volume to maintain a positive reputation, and sudden large bursts after long periods of inactivity can severely harm their standing.

Can inconsistent high volume damage a dedicated IP's reputation?

Yes, it can. Mailbox providers expect a consistent volume from dedicated IPs. Large spikes after periods of dormancy can be seen as suspicious activity, leading to deliverability issues or even blocklisting .

What is a hybrid IP strategy for varied sending patterns?

A hybrid approach works well: use a dedicated IP for any consistent, lower-volume sends (like transactional emails) and shared IP pools for your large, infrequent campaigns. This isolates the risk of your large bursts from your primary email stream.

Should I still batch my sends when using shared IPs for high volume?

Even with shared IPs, it's advisable to spread out your large sends over several days instead of sending them all at once. This helps to distribute the volume and further reduce the chances of triggering spam filters due to sudden, massive traffic.

What are the best practices for maintaining deliverability with inconsistent sends?

Focus on excellent list hygiene, ensure all emails are properly authenticated (SPF, DKIM, DMARC), and actively monitor your IP and domain reputation. These practices are crucial regardless of your IP type and can significantly improve your email deliverability .

When should I use dedicated IPs vs shared IPs for inconsistent, high-volume email sends? - Sender reputation - Email deliverability - Knowledge base

When managing email campaigns, a crucial decision often arises: should you opt for a dedicated IP address or use a shared IP pool? The common wisdom typically points to dedicated IPs for high-volume, consistent senders due to the control they offer over sender reputation. However, many email programs don't fit neatly into this consistent mold.

The real challenge emerges when you have very high volumes, perhaps millions of emails, but they are sent inconsistently, such as once a month or even less frequently. This sporadic sending pattern can complicate the benefits traditionally associated with a dedicated IP.

My goal here is to help clarify which IP type is best suited for scenarios involving high-volume, inconsistent email sends, and to explore strategies to maintain strong deliverability under such conditions.

Understanding IP types and their impact

A dedicated IP address is exclusively yours, meaning your sender reputation is solely dependent on your sending behavior. This gives you complete control over your IP's standing with mailbox providers. It is often recommended for businesses that send large, consistent volumes of email, as it allows them to build a robust and independent sending reputation over time.

Conversely, a shared IP address is used by multiple senders. The reputation of a shared IP is influenced by the aggregate sending behavior of everyone using it. This can be beneficial for new senders or those with low to moderate volumes, as the collective good behavior of other senders in the pool can help protect your deliverability. However, it also means you are vulnerable to the poor sending practices of others.

IP reputation is a critical factor for email deliverability, influencing whether your emails land in the inbox, spam folder, or are rejected entirely. Mailbox providers assess an IP's reputation based on various metrics, including spam complaints, bounce rates, and sending volume consistency. A positive reputation ensures your emails are trusted and delivered promptly, while a poor one can lead to significant deliverability issues.

Dedicated IP

Control: You have full control over your sending reputation.
Warm-up: Requires a significant IP warm-up period to build trust.
Consistency: Best for consistent, high-volume sending to maintain reputation.

Shared IP

Control: Reputation is shared with other senders in the pool.
Warm-up: IPs are generally pre-warmed by the provider.
Consistency: Suitable for inconsistent or low-volume sends due to shared burden.

The challenge of inconsistent, high-volume sends

The core issue with using a dedicated IP for inconsistent, high-volume sends is the concept of a cold IP. Mailbox providers expect a relatively consistent volume from a dedicated IP address. Sudden spikes after long periods of inactivity can flag your IP as suspicious, akin to a spammer trying to send a large volume of unsolicited mail. This can severely damage your sender reputation and lead to emails being rejected or sent to the spam folder.

Mailbox providers are cautious about large volumes from IPs that haven't established a consistent sending history. If your dedicated IP sits dormant for weeks or months and then suddenly sends millions of emails, it’s a red flag. This behavior doesn't align with what providers typically expect from legitimate senders and can trigger their spam filters.

This pattern significantly increases the risk of your dedicated IP landing on a blacklist (or blocklist). Once your IP is on a blocklist, your deliverability will plummet, and the process of getting delisted can be time-consuming and challenging. For this reason, if your sending volume is truly inconsistent, a dedicated IP might not be the optimal choice unless you can maintain some baseline level of activity, or spread out your sends significantly.

Inconsistent sending warning

Sending large, inconsistent volumes (e.g., 1-2 million emails once every few months) from a dedicated IP can be detrimental to your sender reputation. Mailbox providers might view these sudden bursts after long periods of inactivity as suspicious, leading to increased spam complaints and potential blocklisting, regardless of your content quality or list hygiene.

Strategic choices for inconsistent high volume

For situations with inconsistent but very high volume, a shared IP pool often proves to be the better option. Shared IPs are continuously used by many senders, maintaining a consistent traffic pattern that helps to mask individual sender's fluctuations. This means your large, infrequent sends will blend in with the regular traffic, reducing the likelihood of being flagged for unusual volume patterns.

Even when using shared IPs for massive, infrequent campaigns, it's a good practice to distribute these sends over several days rather than unleashing them all at once. While shared IPs offer some buffer against inconsistency, staggering your sends can further mitigate potential issues and ensure a smoother delivery process. This is particularly relevant if your volume exceeds typical shared pool limits, or if you want to be extra cautious.

In some cases, a hybrid approach can be most effective. If you have a consistent, albeit lower, volume of transactional or regular marketing emails, a dedicated IP might be suitable for those. Then, for your massive, inconsistent campaigns, you can leverage shared IP pools. This allows you to maintain control over your primary sending reputation while safely delivering large, sporadic bursts without damaging your dedicated IP. Learn more about when to use a shared IP address for email sending.

Sending Pattern	Volume	Recommended IP Type	Reason
Consistent High	100k+ daily	Dedicated	Full control, builds strong independent reputation.
Consistent Low/Medium	<100k daily	Shared	Leverages collective reputation, no warm-up needed.
Inconsistent High	Millions infrequently	Shared (or Hybrid)	Avoids cold IP issues, blends with consistent traffic.
Transactional	Variable, often low	Dedicated (or Shared for very low)	Critical for timely, reliable delivery to engaged users.

Maintaining reputation with strategic IP use

Regardless of whether you choose a dedicated or shared IP, maintaining excellent list hygiene is paramount. Sending to a clean, engaged list reduces bounces and spam complaints, which are critical factors in maintaining a good sender reputation. Regularly cleaning your lists by removing inactive or invalid addresses should be a continuous practice.

Monitoring your IP reputation is also essential. Tools like Mailgun's blog and Klaviyo's help center provide valuable insights into deliverability. Additionally, implementing strong email authentication protocols like DMARC, SPF, and DKIM is crucial for verifying your sending legitimacy and preventing spoofing, which indirectly affects your IP's reputation.

For inconsistent, high-volume sends, the decision between dedicated and shared IPs isn't always straightforward. It often comes down to balancing control with the potential for reputation damage. Carefully assessing your sending patterns and leveraging the right IP strategy will be key to maintaining robust email deliverability.

Views from the trenches

Best practices

Maintain strict list hygiene to reduce bounces and spam complaints, regardless of IP type.

Segment your audience carefully to send relevant content, improving engagement and deliverability.

Ensure proper email authentication, including SPF, DKIM, and DMARC, for all sends.

Monitor your sender reputation regularly using available postmaster tools.

Common pitfalls

Not properly warming up a dedicated IP before sending high volumes of email.

Sending sudden, large bursts of email from a dedicated IP after long periods of inactivity.

Neglecting to monitor IP and domain reputation, leading to undetected deliverability issues.

Failing to clean email lists, resulting in high bounce rates and spam trap hits.

Expert tips

Consider a hybrid IP strategy: dedicated for consistent, lower volume sends and shared for massive, infrequent campaigns.

If using a dedicated IP for inconsistent sends, try to maintain a low, consistent baseline volume to keep it warm.

Spread out large, inconsistent campaigns over several days, even when using shared IP pools, to reduce sudden load.

For extremely high and inconsistent volumes, explore IP rotation strategies if offered by your ESP.

Marketer view

A client sends tens of millions daily on dedicated IPs, but their quarterly mailings of almost 100 million are sent through shared pools at their ESP.

2021-11-09 - Email Geeks

Marketer view

This strategy of using shared pools for large, inconsistent sends is something I definitely use.

2021-11-09 - Email Geeks

Key takeaways for your sending strategy

Ultimately, the choice between dedicated and shared IPs for inconsistent, high-volume email sending hinges on a careful analysis of your specific sending patterns and risk tolerance. While dedicated IPs offer ultimate control, they demand consistent volume to maintain a healthy reputation. In contrast, shared IPs provide a more forgiving environment for sporadic bursts, leveraging the collective reputation of other senders. By understanding these dynamics and potentially adopting a hybrid approach, you can optimize your email deliverability even with challenging sending behaviors.