The Role Of ESPs In Email Deliverability


Our Deliverability Team gets questions like this all the time:

  • “Why is my bounce total higher in ESP X?”
  • “Why are my open rates lower when I switched to ESP Y?”

These are excellent questions. In the email industry, deliverability and engagement rates are key. If people aren’t receiving the email and acting on it, what’s the point?

But when comparing and trying out a new email service provider (ESP), you have to expect differences in your engagement rates. The kicker is to know what these differences mean and how to accommodate for them.


Calculating Engagement

The most obvious difference between the open or delivered rate is how the ESP defines those terms. For example, GetResponse will count someone who clicked toward your open rate, since that’s evidence they’ve opened the email as well.

There’s also different formulas for open and click rate, which can vary if you’re calculating the opens out of the “sent” total (total of original recipients) or the “delivered” total (total of original recipients minus bounces). GetResponse calculates your engagement rates based on what actually delivered.


Bounce Processing

A less obvious difference is in how the ESP processes and categorizes bounces. Since many receivers send unclear or deceptive bounce replies, ESPs fine-tune their bounce processing to make sure responses are categorized correctly. This means that often a “bounce” in one ESP may be classified as a “delivery” in another.

For example, a bounce reply with the code “550” should be a hard bounce, but if the receiver sends “550 please try again later”, an observant ESP should adjust bounce processing to make sure messages like this are attempted again. Of course our hardworking Deliverability Team pays attention to these details to give you the most accurate message statistics possible, but it may mean you see more or less bounces if you’re trying out multiple ESPs.


GetResponse Marketing, Email Marketing, Content Marketing, Automation, Deliverability, Email Open Rate, CTR, ESPs, Email Service Providers, Click Through Rate


Content Fingerprinting

Believe it or not, your email content has an identity of its own. A content’s “fingerprint” represents any combination of sender info, phrases, URLs, footer info, image hosting, etc. that when fit together easily identifies you as a sender. This means that even if you’re using a new IP, many receivers might still recognize your content as something they’ve seen before.

Sometimes this is a really good thing. If a subscriber has been highly engaged in your content, its fingerprint may keep that email going to their inbox even after you’ve switched IPs.

But sometimes this is a bad thing. Receivers were used to you sending over a specific range of IPs, but now the IPs have changed. Is this really you? Are you trying to hide from something by changing IPs? To be cautious, some receivers may (at least temporarily) send more of your messages to the spam folder.

To help combat poor deliverability, I can’t recommend enough to try A/B testing. If you’re looking for more than just opens and clicks (maybe purchases, replies, etc?), GetResponse lets you choose to manually review and select the “winning” content, giving you tons of insight into both the preferences of your subscribers and spam filters. With your most engaging content, a new ESP’s good reputation can help boost your deliverability instead of bringing it down.


IP Reputation

Obviously when you switch ESPs, you’re now sending over a different set of IPs. This reputation is a lot like the reputation we build as people — it’s based on things you’ve done in the past and who you’re associated with. For an IP, receivers are looking to see what kind of email it’s sent in the past and what other IPs associated with it are doing. Of course every ESP has a different reputation, and you’ll probably send over different IPs throughout the life of your account.

At GetResponse, the IP you’re sending over is shared by other GetResponse users, all under the “” domain. Our Compliance Team does an amazing job keeping only good senders in our system, and that’s given us a good reputation with receivers. On top of that, our Deliverability Team monitors blacklists and bounce reasons to make sure each IP is performing at its best. We’re constantly communicating with receivers and our partners in anti-abuse to keep on top of industry standards and innovations. GetResponse customers will be able to use this good reputation to their advantage.

Just remember that there are some drawbacks to switching to an ESP with a better reputation. It could result in more unsubscribes and spam complaints, since those messages are now arriving in more inboxes for people to “negatively” engage. A better reputation means more visibility into what needs improving.


The Takeaway

Yep, this link has a really huge number on it, but it’s the truth. For customers using our shared IPs without any compliance-related issues, we see a collective deliverability rate of over 99%. I know. It gives me goosebumps sometimes too. So, I’m happy to give away the secret recipe for amazing deliverability:

Rather than trusting the results of a few test sends, look for an ESP with a knowledgeable Deliverability Team and a responsive Compliance Team. I know I’m “tootin’ my own horn” here but, it’s these factors that will keep your deliverability rates dependable and be able to offer you actionable advice for the future.


What do you think?

What do you think? We’d love to hear from you. Leave a comment and tell us what you think.

Email Deliverability From A To Z Guide

Email Deliverability From A To Z

Download our free guide and learn how to make sure that your deliverability is pitch-perfect with tips from a deliverability manager at GetResponse. Nurture relationships, learn how to tackle list building, and make sure that the content you send doesn't raise up any flags.

  • Thanks Anna! This article is really explanatory. 🙂
    What I’m trying to find out at this moment, is what kind of bounce message an ESP gets when the problem is a poor reputation. I’ve never seen a bounce message saying “email not delivered to recipient since you’re a spammer.” 😉 Or anything similar.
    We are now in the middle of a deliverability discussion with a new ESP due to having received a higher bounce rate.
    Thank you! 🙂

  • Anna

    When it comes to reputation-based bounces, you might see bounces related to the content like “message detected as spam”, “spam message rejected”, “mail content denied”, etc. You may also see some related to the IP, like “IP is blacklisted”, “rejected IP”, etc. Technically a receiving server can create any bounce text it wants, so my years in this industry have seen a lot of variations!

    Most reputation-based bounces are caused by abuse complaints (someone on the receiving end telling their mailbox provider that this message is unwanted). By being clear to new subscribers about (1) who you are and (2) the specific kinds of content you’ll be sending them, reputation-based bounces should remain rare. 🙂

  • Thank you Anna! 🙂

  • Hi Anna, just want to thank you too for this detailed explanation. There are many things I didn’t know about this subject.

    Two days ago we sent an email that went to the spam message folder of many users (I knew that after seeing open rates) and was really surprised, as I have never had any similar problems with GetResponse for 2 years, and I’ve been sending some emails per week to a growing +20,000 subscribers list.

    GR Deliverability Team is checking this issue (actually, they pointed to me this article of yours), but I did some tests and would like to share some of the results with you as well, in case you have any other ideas or thoughts about this, as they seem weird to me:

    1. When sending an email with or without links through GetResponse with certain subject lines, it goes to spam
    2. When changing subject line on GetResponse and not using any ‘marketing words??’ in Spanish like “marketer, story, project, business…”, it doesn’t go to spam
    3. When using bullet points within the text with a “correct” subject line (in GetResponse), it goes to spam
    4. Today we’ve sent an email using one of these words (‘presentaciones’) and it didn’t go to spam

    Thanks again!

  • Anna

    Hmm, this is a pretty complex situation. Unfortunately I won’t be able to diagnosis the issue from here, so my recommendation is to keep working with the support team. They’ll be able to take a in-depth look into past statistics, run tests, and present some actionable steps. I’ll keep a look out for your ticket!