Is it common for agencies to use one ESP with separate IPs per client, and does it impact email deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 31 Jul 2025
Updated 19 Aug 2025
6 min read
When an agency manages email campaigns for multiple clients, a common question arises: is it standard practice to use a single email service provider (ESP) but assign separate IP addresses to each client? This setup might initially seem unusual if you're accustomed to each client having their own distinct ESP instance. However, it is indeed a fairly common model, especially for larger agencies.
The key considerations for this approach revolve around operational efficiency and, critically, its impact on email deliverability. Each client's email program is distinct, and the reputation associated with their sending IP directly influences whether their messages reach the inbox or land in the spam folder. Understanding how this model affects your clients' sender reputation and overall deliverability is essential.
The agency ESP model and its prevalence
Many agencies opt to consolidate their clients within a single ESP, leveraging the benefits of a master account with sub-accounts or white-label solutions. This approach allows agencies to manage diverse client needs, from different sending volumes to varied campaign types, all under one roof. The ESP's platform often provides the necessary tools to segregate client data and campaigns effectively.
This centralized model offers significant operational advantages. Agencies can streamline their workflows, standardize reporting, and develop deep expertise with one platform's features, rather than managing multiple disparate systems. This can lead to economies of scale in pricing and more efficient resource allocation within the agency.
The prevalence of this model stems from its flexibility. ESPs have adapted to offer features like distinct sub-accounts, separate IP addresses, and custom domain configurations for each client, even within a shared infrastructure. This allows agencies to maintain brand separation and deliverability independence for each client while benefiting from a unified backend.
Dedicated IPs versus shared IPs for agencies
A crucial decision for agencies using a single ESP for multiple clients is whether to assign dedicated IP addresses to each client or utilize shared IP pools. This choice profoundly influences deliverability and reputation management. Dedicated IPs mean that only a single client's sending behavior determines the IP's reputation, offering greater control but also requiring consistent high volume to maintain a warm IP.
Conversely, shared IPs involve multiple senders using the same IP address. While this can benefit low-volume senders by allowing them to "piggyback" on the collective good reputation of other senders in the pool, it also carries the risk of being negatively impacted by the poor sending practices of others. An agency must carefully consider each client's sending volume and reputation needs when deciding between these options.
The optimal choice often depends on the individual client's sending profile. High-volume senders with consistent email streams are typically better suited for a dedicated IP. For clients with lower sending volumes or infrequent campaigns, a shared IP pool, if well-managed by the ESP, can be a viable and cost-effective solution. This article on When to use dedicated versus shared IPs for email, an external resource.
Dedicated IP addresses
Reputation control: Full control over IP reputation based solely on your client's sending behavior.
Volume requirement: Requires consistent high sending volume to maintain a warm, reputable IP.
Isolation: Sending issues of one client do not directly impact other clients.
Setup complexity: Higher initial setup and warming effort for each new IP.
Shared IP addresses
Cost-effective: Generally more affordable, as the cost of the IP is distributed among many users.
Warmth: IPs are typically pre-warmed by the ESP, beneficial for low-volume senders.
Reputation risk: Reputation can be negatively affected by other senders in the pool.
Less control: Limited control over the overall IP reputation, reliant on ESP's management.
Impact on email deliverability
Using separate IP addresses per client within one ESP can significantly influence deliverability. Each IP develops its own sender reputation with internet service providers (ISPs) like Gmail, Outlook, and Yahoo. This reputation is built over time based on factors such as bounce rates, spam complaint rates, email content, and adherence to email authentication standards.
For agencies, this means that while one client's campaigns might be landing in the inbox consistently, another client's campaigns, even from the same ESP platform, could face blockages or land in the spam folder due to their distinct IP reputation. It emphasizes the need for meticulous management of each client's sending practices. Poor sender reputation can severely impact inbox placement, as detailed in this How email sender reputation impacts inbox placement, an external resource.
Email authentication protocols like SPF, DKIM, and DMARC are crucial regardless of the IP setup. Agencies must ensure that each client's domain has these records correctly configured for their assigned IPs within the ESP. Proper authentication helps ISPs verify that the emails are legitimate and not spoofed, which is a foundational element for good deliverability. Learn more about how these records affect how deliverability is affected.
Common deliverability pitfalls with agency IP separation
Inconsistent sending volume: Low or erratic sending volumes on a dedicated IP can lead to a cold IP, triggering spam filters.
Lack of ongoing monitoring: Without continuous monitoring of each client's IP and domain reputation, issues can escalate unnoticed.
Ignoring client list quality: Sending to unengaged or old lists, even with separate IPs, will still harm the specific IP's reputation.
Insufficient warming processes: New dedicated IPs for clients require a careful warming period to build trust with ISPs.
Operational efficiency and best practices for agencies
Beyond deliverability, using a single ESP with separate IPs per client offers significant operational efficiencies for agencies. It simplifies staff training, as teams only need to master one platform. It also centralizes billing and potentially provides better support from the ESP due to the consolidated volume. This unified approach can lead to quicker campaign launches and easier troubleshooting.
To mitigate deliverability risks and maximize efficiency, agencies should implement robust internal processes. This includes strict list hygiene practices for every client, consistent monitoring of campaign performance, and proactive management of IP and domain reputations. Regularly auditing client sending practices is paramount to prevent one client's issues from indirectly impacting the agency's overall standing with the ESP.
Crucially, agencies must effectively manage IP reputation for different clients. This means understanding that even with separate IPs, shared infrastructure elements or agency-wide sending policies can have a subtle impact. Proactive blacklist (or blocklist) monitoring for each client's IPs and domains is vital. If you're concerned about your IPs ending up on a blacklist, our blocklist checker can help.
Factor
Impact on deliverability
Agency best practice
IP reputation
Directly affects inbox placement for each client.
Monitor reputation via tools like Google Postmaster Tools.
Domain reputation
Influences overall trust of client's sending domain.
High bounce and complaint rates destroy reputation.
Regularly clean lists to remove invalid or unengaged subscribers. Avoid spam traps.
Views from the trenches
Best practices
Establish a clear process for onboarding new clients, including IP warming and DNS setup.
Implement strict list validation and hygiene protocols for all client lists.
Regularly review deliverability metrics for each client's campaigns, including opens, clicks, bounces, and complaints.
Ensure proper email authentication (SPF, DKIM, DMARC) is configured and monitored for every client's sending domain.
Common pitfalls
Assigning dedicated IPs to low-volume clients, which can lead to cold IP issues and poor reputation.
Neglecting to monitor individual client IP and domain reputations, leading to unnoticed blocklistings.
Failing to educate clients on the impact of their content and list quality on deliverability.
Not having a robust system for separating client data and preventing cross-contamination within the ESP.
Expert tips
Consider the ESP's white-label capabilities and sub-account management features when choosing a platform.
For transactional emails, it may be beneficial to use separate IPs from marketing emails to protect reputation.
Maintain transparent communication with clients about their deliverability performance and any issues.
Continuously educate your team on the latest email deliverability best practices.
Expert view
Expert from Email Geeks says that this agency model is fairly common, having seen many clients white-label ESPs.
2019-09-12 - Email Geeks
Marketer view
Marketer from Email Geeks mentioned that as long as there are good controls to prevent mixing client data, the setup is just a tool for the job, especially since agencies might get good ESP support due to their volume.
2019-09-12 - Email Geeks
Optimizing deliverability in agency ESP models
The practice of agencies using a single ESP with separate IP addresses for each client is indeed common and, when managed correctly, does not inherently harm email deliverability. The critical factor lies in meticulous management of each client's sending reputation, distinct IP warmth, and adherence to email authentication standards.
Agencies can leverage the operational efficiencies of a consolidated ESP while providing clients with the dedicated reputation control needed for optimal inbox placement. This requires robust internal processes, continuous monitoring, and strategic decisions regarding dedicated versus shared IP usage based on each client's unique sending profile. By focusing on these elements, agencies can ensure strong deliverability across their diverse client portfolios.
Google Postmaster Tools.
