Luke Glasner on the Email Metrics That Really Matter in 2025 – And How to Improve Them

Quick Answer

What’s the most important thing for email marketers to focus on?

Short answer: Keep your list clean and pay attention to all your metrics—but especially revenue per email (RPE) and spam complaints. A healthy list gets you to the inbox, and RPE shows what drives real results, while keeping spam complaints low protects your sender reputation.

Why it matters: If your list is full of inactive or fake addresses, your deliverability suffers, and your emails don’t reach the people who matter. Tracking all metrics helps you understand engagement, but focusing on RPE and spam complaints ensures you’re driving value and staying in the inbox. Small tweaks in opt-ins, form validation, and list management can make a huge difference over time.

Few people know email inside out like Luke Glasner. With more than 20 years in the game, he’s done it all – from hand-coding campaigns to helping set the very standards for how email metrics are measured.

In this conversation, Luke breaks down the numbers and strategies that matter most today. He explains why metrics still fascinate him, how email deliverability has shifted in recent years, and the practical steps marketers like you can take to keep subscribers engaged.

In this interview, you’ll learn:

• Why email metrics like revenue per email (RPE) are more important than ever
• How to keep your subscriber list clean and engaged
• How smart opt-in processes and engagement strategies can boost results
• Tools and tips to understand your sender reputation and improve performance
• Why content and URL reputation still shape deliverability outcomes

You can also watch the video of the Luke Glasner interview below.

Luke, you’ve been involved in all parts of email. Is there a part of it that you find the most fascinating?

A lot of people in the email space know my work around metrics, and that’s been one of the big areas that I’ve been very involved in over the years and of course, throughout my entire email career.

I also really like email deliverability.

Obviously, I am very excited about coding emails as well, which is something that you just don’t see as much anymore as when I first started, but a good coder can make an email really shine.

Well, what is it about the metrics? What interests you about that?

When I started, the thing that was getting me about metrics was the fact that there was no real standard for email metrics back in the day in the early 2000s.

I led a project at the Email Experience Council, which has since undergone several name changes. The project was called the SAME Project, which stood for Support Adoption of Metrics for Email.

We brought together over 30 email service providers (ESPs) from around the globe to come up with industry standards for email metrics measurement.

The project showed some maturity of the email industry. It showed we had become a powerhouse and a mature industry because we actually have metric standards for how things are calculated.

I used to describe it as, imagine if when you got in your car and you typed in an address for your GPS, if everyone counted the distance of a mile slightly differently.

While directionally we’re all going in the right direction, you may be missing turns because everyone’s map isn’t the same.

So that’s something I worked on and was really proud of.

I like the metrics of email because there’s that famous quote by Mr. Wanamaker, “I know half of my money on advertising is wasted, but I don’t know which half.”

The thing about email metrics is it tells you where the waste is and what is working.

It really allows for a wonderful environment for you to conduct testing, improvement, benchmarking, and things like that. And that applies to all email, not just campaign data; you can use the same type of benchmarking.

Am I improving my inbox placement? Also, am I reducing my spam complaints? Am I doing better at deliverability?

So it’s all measurable, and things that get measured tend to matter.

And that’s a lot about my love for email metrics!

The importance of Revenue Per Email (RPE)

Have you seen the way people view metrics and what they measure change through the years?

Yes. In fact, we have dramatically changed in things like open rates, which when I started, was a very big thing to calculate, talk about, and focus on.

However, with features like Apple MPP, open rates are no longer as reliable as they were in the past. So it has moved away. People are moving away from opens and focusing more on metrics that matter, which also include clicks.

I’ve also seen a big rise in bot clicks – or I like to call them filter clicks – where different systems will go through the link to check for, say, if there’s a virus attached to the end of it; those can sometimes show up in your reports.

So those two metrics have lost a bit of their accuracy over my time.

The other big shift I’ve seen is that email marketers are now focusing on metrics that matter. You need to focus a lot more on business KPIs.

If somebody opens an email, there is value there, there are brand impressions there, but if it’s not resulting in conversions down the line, it’s just not where you should be focusing.

In fact, that brings me to one of my favorite metrics, which is revenue per email or RPE.

If there was any metric I would say you should watch and use for testing, it’s that one.

That’s very interesting because I don’t see RPE mentioned nearly as much as some of the others.

Yes.

We tend to focus on the metrics that are reported within our ESP. So those are your standards: open, click, unsubscribe, bounce, and spam complaints.

And from an email deliverability perspective, I also want to focus on my second favorite metric, which is spam complaints.

If you’re getting a lot of spam complaints — and “a lot” is roughly more than one per thousand, so it is a tiny number — that is the quickest way to end up in the junk folder.

So you really need to be laser-focused on that and pay attention to it, and keep it as low as you can.

Luke, how do you think someone can make their opt-in process better?

Well, there are two things they can do.

They, of course, can do real-time validation, which is something ZeroBounce does. So this is when it checks the email address while they’re filling out a form.

That reduces junk coming into your forms, it reduces bot sign-ups, and it makes sure they didn’t make a typo. Maybe they typed a dash instead of a dot, or “Gnail” or “dot-con” at the end of their address.

If you’re not checking them, it’s quite possible that you now had someone that was interested, but you lost them due to a simple typo. That’s one of the ones that’s very important.

Try the ZeroBounce real-time email verifier

The other thing is to secure your forms with things like a CAPTCHA because the amount of bot sign-ups and form attacks I have seen in the past two to three years has exponentially grown.

I don’t have a study to cite, but from my own experience working with clients, I’ve never seen as many fake sign-ups as I’ve seen in the past two years. It’s the most out of my 20-plus-year career.

“Content does matter.”

What misconception about email do you find persists?

One – and it’s related to deliverability – is what people think of when they think of content filtering.

There is no rule that if you say “free” or use this word, you’re gonna go to the spam filter. That’s not really how those things work.

However, what people don’t tend to know or check about is a way that content does matter. And that is the reputation of all the URLs within your email.

So if you have a link to a dodgy site or maybe you’re hosting images with somebody and they’re not your own site, if the reputation of that image host is bad, that can drag down your whole email’s ability to reach the inbox.

So content filtering isn’t really so much about whether I used a specific word – that’s a myth. But content and structure do matter, and it’s much more about the reputation of the URLs and how you properly form the email.

And of course, if you didn’t do a good job at making the email, it’s not gonna look right across clients.

Email marketers know that – Outlook, especially, can be difficult to make the email display properly. It is both a science and an art to be able to make the thing look right across all the different clients.

Most web developers have to deal with maybe five or six major browsers; email marketers deal with 90-plus email clients, every one of which makes it look slightly different.

When those things break down, engagement breaks down.

And when engagement starts to fall because of a bad customer experience, your ability to reach the inbox will follow suit.

You have undoubtedly looked at a lot of emails through the years.

Clever ways to increase email engagement

Have you seen a brand or a company where you thought, now these guys over here, they get it!

Yes. There are lots of them out there. One that I liked a lot was Torrid.

They tied clicks back to their loyalty program. So if you opened and clicked in an email – one of the ones that they sent that day – you would get a point in their loyalty program. If you get enough points, you get a small token of appreciation, a reward.

So I think it was, if you got 100 points, you got $5 when it first came out as a reward in the loyalty program. To look at that another way, they paid $5 to get you to click 100 times. And I am subscribed to their emails, though I don’t buy a lot of plus-size women’s clothing.

But what I did find was that because I was opening these emails all the time, just so that I could click to get my points — because I’m that type of person — it worked.

I ended up buying gifts for other people a lot more often than I would have shopped there simply because I was trying to get the loyalty point.

You can see engagement devices in this in a lot of emails where you see the thumbs up and the thumbs down. Did you like this email? Did you rate this email?

So, look for ways to allow feedback within the email by having them click. It doesn’t necessarily have to be tied to a reward. People like to express their opinions about email.

That is one way to allow them to do that. And then that creates engagement and it creates stickiness for your emails.

What is an email marketer’s most valuable resource?

I would say their most valuable resource is the list and keeping it clean.

Because if you don’t have a good list, if your list is dirty, you’re not gonna reach the inbox. And that’s not just for the people that you have a bad address in there for, but it’s for everything.

So the quality of your list and your ability to use its data is probably one of the most important assets for email.

A good list will outperform a bad list every day, and a smaller good list will outperform a huge list because it reaches the inbox while the vast majority of the other one doesn’t.

I’d rather have a hundred people that are truly interested and likely to buy than a thousand people that view my emails with apathy. They don’t care.

There is value to always being in their inbox, but I do think that the quality of the subscribers plays a big role.

Having ways to keep the list clean, validating people not only when they come in, but checking up on them again is a great way to keep the list clean. But also take a look at things like, how long does a person last? When should I activate re-engagement?

A lot of people used to just use some best practice like, if it’s been six months or nine months, send them the re-engagement.

My view on that is that if the person has already stopped engaging with your emails, the re-engagement effort will likely fall flat because they’re already ignoring you.

So understand the lifespan of a subscriber and then get out ahead of that, so that before the person disappears is when you start to re-engage them, when you might convert them with a win-back type offer or something like that.

Don’t wait till they’re totally gone because the chances of you re-engaging them become slimmer and slimmer the longer it’s been.

“Email deliverability has gotten harder.”

Is email deliverability complicated? How do you think a marketer or a company should approach it? How should they feel about it?

I would say that email deliverability is complicated, and it has gotten harder as the years have gone by.

The sender guidelines that came out last year from Yahoo and Google, and then we watched Microsoft and Apple also jump on the bandwagon with very similar sender guidelines. While they are clearly communicated in their FAQs, it’s not easy to do some of the things they say.

For example, they’re like, keep your spam complaints under a threshold of 0.3%, and the recommended threshold is 0.1%. That works out to one out of a thousand. But that’s not necessarily easy to do.

A lot of the ISPs won’t tell you who complained; they just tell you that they did. Google, for example, tells you that people marked you as spam, but they don’t tell you who. So it’s not like you can go, “well, that was the guy that marked me; let me go suppress them.” It’s often not that simple.

The other thing is the technical setup. Not everyone gets the ins and outs of how SPF and DKIM work.

If you know how, yeah, it’s easy. I post a DNS record, and I know what all the things in it do.

But if you don’t know that stuff, it can be a little scary. People don’t like to mess with DNS records. If you make a mistake, you break the website, or you break the mail server.

So it’s important to understand what you’re doing and how those work. And I think that that can be hard for different marketers to address. That’s not really in their day-to-day. So it may be something that they don’t really know about, or maybe they’re just nervous about it.

And I will say out to all the email marketers, everyone, even those of us who have been around for a very long time, everyone sweats it when they hit the send button. I remember MailChimp used to have the monkey finger that came down over the send button, and you could see the hand was sweating.

What I will say is this: no one that has ever worked in email for any length of time has had a 100% campaign rate. Everyone makes an error at some point. So have a plan for when that’s gonna happen and a way to react in a good way to it.

“Cleaning the list is a great start, but it goes beyond that”

People say to me: “well, I’ve cleaned the list. Isn’t that enough?” What do you say to that?

Cleaning the list is a great start, and it’s important to do the list hygiene, but it goes beyond that. You need to segment the list to find the different types of content, the types of creative that will resonate with that particular segment.

Once your list gets to be in the thousands, it’s not like there’s any way for you to personally know everyone on the list anymore.

A lot of people maybe started a newsletter or something when they start the store; it’s like their early customers, it’s family and friends, it’s people they actually know, so they have a good idea of who they’re writing to.

But as you scale, once you get to hundreds of thousands, millions of people on the list, all those people’s needs are gonna be different. So you don’t want to send them the same thing. And that’s where segmentation and profiling come in.

You can segment based on virtually anything in email. There’s a lot. Whatever data you have in that ESP, you can probably build a segment around it. But there are different ones that you want to do. For example, first-time customers, repeat customers, prospects, and various profiling techniques.

For example, I like to use cluster analysis. You find people that naturally kind of form their own natural subscriber segments because they’re similar people.

Once you have a good profile of the person, you can then build content, creative, frequency strategy around reaching those different people.

“Take advantage of free resources.”

If somebody or their company is just starting to dip their legs in the water of deliverability, what would you say is a starting point?

Get some data and some insight and tools around your deliverability.

We have a wonderful ZeroBounce ONE package that has all of our tools in it, along with validation credits every month. It’s very affordable, only $99. That’s cheap enough that virtually anyone can do it.

Learn more about ZeroBounce One

But also take advantage of free resources.

Virtually any sender can sign up for Google Postmasters. It’s domain-based, so you don’t need to have your own dedicated IP. Microsoft SNDS is also very good, again, also free, but you do need a dedicated IP in order to be able to do that.

So not everyone, especially smaller mailers, can actually use that, whereas Postmasters, everyone can use it, and it will show you things like the compliance dashboard.

Since most of the major mailbox providers all use basically the same sender guidelines, that’s a good way to check: am I meeting all the requirements for bulk senders? For example, does my list unsubscribe header work? Am I honoring unsubscribes quickly?

Yes, you can look at spam complaints there, but of course, those are specifically for Google, for Gmail. And if you use Microsoft, you can look at theirs.

I also like that they give reputation, sender rep, where they rate you from bad, low, medium, or high. Obviously, everyone wants to be at the top of the line in the green.

If you think about what the colors mean, it’s a traffic light: red is stop, there’s a problem here; yellow, medium, be cautious; green is everything’s going good. Hit the gas pedal and keep going.

But that is a good way to get started with understanding what your sender reputation is, and it’s free, and everyone can do it. It’s relatively easy to sign up, and then you just verify the domain, and you’re good to go.

“I’ve never seen anything like ZeroBounce ONE.”

So I can’t resist this question: have you ever seen anything like ZeroBounce ONE?

No, I can answer that really easily. No, I have never.

I have seen deliverability suites before, but they are typically 10 times more expensive.

The other thing I’ve never seen at a lot of companies I worked in over my career is the speed at which we respond to customer ideas, to requests internally. 

“Hey, this person told me about this. Can we build it for them? This would be a great thing to improve our deliverability tools.” And they’ve just been outstanding at getting those things updated and fixed.

Time to verify your list? Try ZeroBounce One

We’re making it better all the time. And there are a lot of tools in there.

I especially like the email server test that checks out all your configuration. It is significantly more robust than many similar checkers and will tell you everything you need to know.

If you see something in there that you need to fix, you can fix it. And if you don’t know how, you can give us a call, and we will certainly help you.

I also really like the Inbox Placement tool because one of the things where people try and do that on their own, they don’t think about how those algorithms work.

Chances are I open a lot of my own, especially if I work in email marketing – I’m probably the person that opens and clicks on the most emails. Most email marketers open every email they send and click every link to be sure that they all go to the right place.

So how you engage with email is very high engagement, whereas other people have low engagement.

One of the things that’s important about an inbox placement test is that it does rotate the seeds on a regular basis. Once they’ve kind of been established, the results tend to repeat themselves. So they get stale basically over time.

And so it’s important to have a tool where those get updated regularly so that you’re getting accurate results on your inbox placement.

Great information.

Well, Luke Glasner, would there be a Luke Glasner theme song? Like, if you were to walk to the plate, what song would they play?

Let’s see. Well, we could go with the baseball analogy and “Put Me in Coach, I’m Ready to Play.” Might be a good song to go for that. Although that’s kind of out of the genres of music I normally listen to. It would probably be some type of alternative or grunge song.

Okay, interesting.

“Here Comes Your Man,” by the Pixies. That might be a good one.

But my last question — I love this question, and I usually apply whatever the person says — How can anyone out there make today better?

Be kind to one another and be understanding. That’s a good way to make today better.

When the people around you, when you’re putting out positivity in the world, and the people around you are feeling that positivity, they respond with positivity to you.

By helping others and being nice to others, you receive help and a boost to your own confidence in return. That’s a good way we can make the world a nicer place.

I like it. I like it. Anything I left out, anything you’d like to leave our viewers and listeners with?

You know, I love to talk about email. So if you have an email problem or an email question, don’t be afraid to go on our site and schedule a call with me.

Not every call has to be a project. I’d be happy to talk to you about any aspect of email based on my years of experience because it truly is a passion of mine and one of the things I truly love to do. Your biggest complaint on a call about email with me is that we might go over time! Schedule a call with Luke and get any email deliverability question answered. Want to clean your list first? You can start for free – create your account now.