How to evaluate an ESP for deliverability before setting it up?
Matthew Whittaker
Co-founder & CTO, Suped
Published 24 Apr 2025
Updated 15 Aug 2025
6 min read
When considering a new Email Service Provider (ESP), a primary concern for many is how it will impact their email deliverability. The idea that one ESP inherently possesses better deliverability than another is a common misconception. While some ESPs may have attributes that contribute to success, a definitive, measurable meaningful way to compare their overall deliverability statistics.
The reality is that your email program's success largely depends on your own sending practices, list hygiene, and content quality. Switching ESPs without addressing underlying issues in your email strategy is often likened to changing gyms to lose weight, when the true determinant is consistent effort and proper technique.
However, this doesn't mean all ESPs are created equal when it comes to enabling good deliverability. It's about how well an ESP provides the tools, infrastructure, and support to help you maintain a strong sender reputation and ensure your emails reach the inbox. Evaluating these aspects before setup is crucial.
The true nature of ESP deliverability
While your domain and sending IP heavily influence your deliverability, the ESP plays a role, especially if you're on a shared IP address. If an ESP doesn't rigorously police the sending behavior of all clients on its shared IPs, your deliverability can indeed be negatively affected by others' poor practices. An ESP with consistently low delivery rates might have a client base that engages in risky sending habits, creating a death spiral for their shared IP reputation.
However, it is more common that a sender with a crappy mail program is blaming their ESP for issues that stem from their own practices. Your mail flow, content, and list quality ultimately dominate your delivery rates. Improving these internal factors is typically more impactful than merely switching providers. You need to understand how to improve your email IP and domain reputation.
The key question isn't Does this ESP have good deliverability? but rather, Is our email program going to thrive on their platform? This shifts the focus from an abstract, often unmeasurable, metric to concrete factors within your control and the ESP's capabilities to support your specific needs. Deliverability issues often arise from changes, such as migrating to a new ESP, making careful evaluation paramount.
Understanding ESP deliverability claims
Many ESPs claim high deliverability rates, but these numbers can be misleading. True inbox placement varies greatly depending on the sender's practices. Focus on the ESP's features and policies that empower your deliverability, not generic, unverifiable statistics.
Crucial questions to ask prospective ESPs
Instead of asking for a generic deliverability score, engage with potential ESPs by asking pointed questions about their operational approach. Inquire about their deliverability team and how they manage reputation across their platform. This is especially important for understanding how they handle shared IP pools.
It's beneficial to request a meeting with the ESP's deliverability support leader. During this meeting, ask detailed questions about their service level options, how they manage ISP communication, and what recommendations they have for your specific email program and needs. Some clients even ask to meet the deliverability representative who would likely be assigned to their account, offering a preview of the ongoing support.
Beyond support, probe into the ESP's technical features. This includes their enforcement policies for problematic senders on their network, their onboarding process, and the availability of features that allow you to control and isolate your sending reputation. This deeper dive will provide a clearer picture than any blanket deliverability claim.
Technical features
Custom domain usage: Ask if they offer custom domains for images, click tracking, and DKIM signing. This can significantly isolate your reputation from other ESP clients.
Dedicated IP options: Understand if a dedicated IP is available and what the criteria are to qualify. Dedicated IPs offer more control over your sending reputation.
Authentication support: Confirm their support for SPF, DKIM, and DMARC setup, as these are foundational for deliverability.
Foundations of email authentication and reputation
Regardless of the ESP you choose, a strong foundation in email authentication is non-negotiable for deliverability. This means properly configuring your SPF, DKIM, and DMARC records. Most major mailbox providers require DKIM authentication for anyone sending through an ESP, and DMARC policies dictate how receiving mail servers should treat emails that fail authentication. Without these, even the best ESP can't guarantee inbox placement.
Pay close attention to an ESP's support for custom domain usage. If an ESP doesn't offer the ability to use your own domain for sending, image hosting, and click tracking, you are neither maintaining nor building your own mailstream reputation to the degree you might want. This can tie your deliverability closely to the shared reputation of the ESP's other clients, making you vulnerable to their poor sending practices.
Your sender reputation, tied to your domain and IP address, is paramount. If you share an IP address with other senders via your ESP, their sending behavior can affect your deliverability. A low sender score or a history of spam can significantly impact your inbox placement. Therefore, understanding the ESP's approach to IP reputation management is critical.
Testing email deliverability before full deployment can provide valuable insights. While it's hard to predict long-term performance, sending test emails to a seed list can give you an early indication of inbox placement and potential spam folder issues. This also helps assess if the ESP's setup process is straightforward for critical authentication mechanisms.
Views from the trenches
Best practices
Actively seek an ESP that offers dedicated deliverability support and resources.
Prioritize ESPs that allow and encourage full custom domain usage for all sending components.
Thoroughly review an ESP's terms of service regarding sending policies and enforcement.
Common pitfalls
Choosing an ESP based solely on advertised deliverability rates, which are often generalized.
Underestimating the impact of shared IP pools if the ESP has lax sending policies for other clients.
Neglecting to configure SPF, DKIM, and DMARC correctly, shifting blame to the ESP.
Expert tips
Ensure the ESP has clear processes for managing IP blacklists and blocklists, and how they communicate listings.
Evaluate the ESP's user interface and documentation for ease of setting up authentication records.
Consider the geographical distribution of their sending infrastructure and how it aligns with your audience.
Marketer view
Marketer from Email Geeks says your deliverability is primarily based on your domain and sending IP, so if you control both, you should be fine. If you are on a shared IP, it's important to ask questions about other companies using the same IP.
2020-07-27 - Email Geeks
Expert view
Expert from Email Geeks says that deliverability issues after switching ESPs are likely due to the sender's mail flow and content, as most ESPs offer similar deliverability if chosen reasonably well. The ESP with consistently low delivery rates probably has problematic customers.
2020-07-28 - Email Geeks
Making an informed ESP choice
Ultimately, evaluating an ESP for deliverability before setting it up isn't about finding a magic bullet. It's about conducting thorough due diligence to ensure the platform provides the necessary infrastructure, tools, and expertise to support your email program's success. Focus on their technical capabilities, support structures, and their approach to managing shared sending environments, especially concerning email blacklists (or blocklists).
A good ESP empowers you with the means to achieve excellent deliverability, but the responsibility ultimately rests with your own sending practices and commitment to email best practices. This approach ensures you're choosing a partner that aligns with your goals and helps you reach your subscribers' inboxes consistently.
