Updated sender guidelines have made inbox placement tougher than ever. When deliverability declines, many businesses instinctively blame their email platform. But is switching platforms really the solution? Can deliverability be compared across different ESPs (Email Service Providers)?
Let’s unpack this.
The Myth of the “Deliverability Test”
It’s common to see blogs comparing ESPs – ranking them based on features, functions, and supposed “deliverability scores.” These comparisons often rely on one-off tests sent to seed lists, which are small sets of test addresses managed by mailbox monitoring services.
That might sound scientific, but it’s not representative. Real deliverability is built over time, across thousands of real inboxes, with genuine engagement data and user feedback.
For an accurate comparison, you’d need to split your actual audience and run long-term campaigns on multiple platforms simultaneously. That’s not practical – and even then, user behavior and engagement would differ enough to skew results.
So, can you compare ESP deliverability? In practice, not really. But this doesn’t mean all ESPs are the same.
The Weakest Link in the Chain
Every ESP claims to fight spam – and many prohibit specific industries in their Terms of Service. But what matters is how seriously they enforce those rules.
When someone clicks “Report Spam” in Gmail or Yahoo, that feedback loops back to the mailbox provider. If enough complaints accumulate, a mailbox provider may block or penalize messages from that IP range.
However, some ESPs reroute that feedback internally. When you click “Report Spam” in the email footer, it may open an internal form rather than returning you to Gmail (that link is different from the built-in “report spam”). That prevents direct mailbox-provider consequences but raises a question: What does the ESP do with that feedback? Do they take action, warn the sender, or quietly ignore it?
That difference can decide whether you’re sailing on a clean network, or one constantly swimming upstream.
Client Vetting: Who Gets In?
At the high end, some platforms rigorously vet every new client before they’re allowed to send. They may review sign-up flows, domain history, and mailing practices to form an “exclusive club” of reputable senders. Because everyone in that ecosystem maintains excellent practices, deliverability across the platform remains strong.
By contrast, platforms offering free or low-barrier access risk higher rates of abuse. Hopefully, they isolate those accounts on separate IP pools, but that’s not always the case.
Pre‑Send Data Screening: Quality Control Before Sending
Some sophisticated ESPs analyze uploaded data before a single email goes out. They may detect invalid addresses, purchased lists, spam traps, or high-risk addresses in the list and can proactively address them.
New users may start with a “starter IP pool” (a probationary period) until they build a positive reputation. In severe cases, users may be suspended before their actions harm the platform.
This proactive screening is invisible to most users but significantly enhances the ESP’s deliverability reputation.
Deliverability Infrastructure: IP Pools and Risk Management
When you hit “Send,” your campaign travels through one or more sending servers, often grouped by IP address pools.
Poorly managed ESPs use a single, shared pool for everyone (a “swamp”) where good senders can sink with the bad.
Better platforms maintain multiple IP pool classes based on clients’ quality scores, as well as pools for transactional emails. Balancing, monitoring, and keeping those pools is a delicate art and a defining trait of a well-run ESP.
Branded Links and Domains: The Silent Deliverability Signal
Even when you authenticate with your own domain, many ESPs still use shared tracking and image domains. That means your links might look like “espname.com/track/1234” – it’s a shared domain that has a good or bad reputation among many senders.
The remedy: use branded domains for tracking and images (example: track.yourdomain.com or image.yourdomain.com). If your ESP supports this, apply it. It’s one of the simplest and most effective ways to reduce “ESP signature” effects.
The Black Box Problem
Most ESPs reveal little to none about what happens behind the scenes. Senders rarely see information about the platform’s IP reputation, infrastructure, or how it allocates resources among clients.
You might not know whether your emails are sent from local servers or from external MTAs (cloud-based MTAs). Transparency varies widely between ESPs – and that’s a key differentiator to consider when choosing one.
So, Should You Switch ESPs?
Changing platforms can help, but only indirectly. If deliverability suffers due to shared IPs, poor client vetting, or a lack of branded tracking support, a move may address structural issues.
But if your data sources, consent, expectations, content, and engagement are dragging your reputation down, moving ESP will not help.
Deliverability is a shared responsibility between the sender and the email platform, but it begins with the sender, not the platform.
Email Deliverability Consultant | Blogger & Podcaster. Helping global email senders, startups, email and digital agencies, and ESPs with email deliverability, email authentication, and strategy.
