advanced email deliverability tactics
Related Categories
Related Courses
Free Resources

5 Advanced Email Deliverability Tactics to Help You Reach the Inbox & Increase Engagement

Are you looking to go beyond the basics of email deliverability?

If you’re familiar with most of the basics behind getting better email deliverability, like…

  • Building (and not buying) a clean list of people who’ve opted in to see your emails
  • Sending to your most engaged subscribers
  • Letting people unsubscribe when they want to

…then this post is for you!

Today, we’re sharing five advanced email deliverability tactics — tactics that usually aren’t discussed in basic deliverability guides. These methods will help you increase your odds of getting your emails seen, opened, and clicked.

Of course, if all of this is new to you, you can read my Eight-Step Email Deliverability Checklist on the DigitalMarketer Blog, which covers the fundamentals of deliverability.

Read our "Eight-Step Email Deliverability Checklist" on the DigitalMarketer Blog, which covers the fundamentals of deliverability.

So, without further ado, here are five expert email deliverability tactics you can use to improve inbox placement and increase engagement.

Advanced Email Deliverability Tactic 1: Suppression Lists

In email marketing, we talk a lot about the importance of who you’re sending to, whether it’s building a clean list or implementing segments so your emails are reaching the most relevant audience.

But who you aren’t sending to can be just as important. "It's a great way to build a good reputation."

At Maropost, we always advise clients to send to their most engaged users first. It’s a great way to build a good sender reputation and reap the rewards of your most loyal subscribers opening and clicking your emails.

We also advise clients to not send to their inactive subscribers — the ones who aren’t engaging with their emails — as another way to boost sender reputation and deliverability.

When you send to subscribers who aren’t engaging with your emails, you risk internet service providers (ISPs) bulking or blocking your emails, preventing you from reaching the audience who actually want to see what you’re sending.

So, how do suppression lists fit into all this?

While you can suppress for anything, from age to gender to previous purchases, inactive suppression allows you to target your inactive subscribers, preventing them from damaging your deliverability.

There’s no universal length of time on when to suppress an inactive subscriber, but there is an easy rule of thumb to gauge when you need to suppress — the higher your send frequency, the shorter the period of time before you suppress.

Chart showing inverse correlation between send frequency and time period before suppression

Inactive suppression is really more of an art than a science, involving a complex balance between suppressing enough to not get bulked by ISPs, while still sending to a large proportion of your list.

Screenshot of what inactive suppression looks like in Maropost

As long as you keep in mind the “golden rule” of email marketing in mind, you can expect to see your deliverability improve.

What’s the golden rule, you ask?

The golden rule of email marketing is to send to people who want to get your emails and not send to people who don’t want to get your emails — you’re emailing your most engaged users and not sending to your inactive subscribers.

Sounds simple enough, right? But as we all know, it’s easier said than done.

You’ll know you’re on the right track with suppression when:

  • Deliverability is at 100%
  • Open rates and click rates are up
  • Complaint rates are down

If you’re not seeing improvement, you’ll want to adjust your suppression rules, usually to make them stricter (a shorter inactivity period before suppression).

Suppression lists are a great way to prevent disengaged subscribers from spoiling your deliverability, but you can always opt to take things a step further, by cleansing your list

Advanced Email Deliverability Tactic 2: List Cleansing

So, what’s the difference between cleansing your list and suppressing it and why choose one over the other?

Suppression lists aren’t as permanent and can be used as a stepping stone to eventually cleanse your list, allowing you to figure out who you might want to cleanse and what your list will look like after.

List cleansing is powerful and, importantly, permanent.

Cleansing your list of inactive subscribers will boost your open rates, but can reduce your open volume. While it’s possible to boost both with a well-executed list cleanse, the usual result is a boost to open rate at the cost of open volume.

But before we get ahead of ourselves, here’s a look at what list cleansing actually involves.

Screenshot Maropost list cleansing tool, and list cleansing in journeys

Let’s say after some experimentation with suppression lists, you find that suppressing people who have been inactive for 90 days yields the best results for increasing engagement, without cutting too much into your list size.

Different email service providers (ESPs) vary in how they handle implementing a list cleansing rule, but in Maropost, you could automate that using the Journeys Tool, so subscribers are automatically unsubscribed from your list if they go 90 days without any engagement.


There’s one final action you should take before removing subscribers from your list — send a re-engagement series.

A good re-engagement campaign is sent out only once to people who haven’t opened or clicked in over 90 days.

(RELATED: The Ultimate Guide To eCommerce Email Marketing (Online Retailers, This One’s For You…))

Let’s say you’ve set up your cleansing rules so subscribers who have not engaged with your emails for 60 days will be cleansed from the list after 90 days. In those last 30 days, you should put them through an automated re-engagement email series to try to regain their interest.

Like this win-back email from Paragon Apparel…

An example of a re-engagement email from Paragon Apparel

Or this one from Zillow…

An example of a re-engagement email from Zillow

And after that re-engagement campaign is sent out, any subscribers who don’t open or click in the next 30 days, it’s safe to say it’s time to remove them from your list.

But engagement isn’t the only factor to consider in list cleansing. You also need to cleanse your lists of any email addresses that may be less than legitimate.

There are two methods to do just that.

Identifying Illegitimate Emails Method 1: Real-Time Email List Cleansing

This method involves checking emails automatically, as people enter them to sign up for your list.

At Maropost, we do our testing on But we suggest BriteVerify, a third-party vendor, as well, which charges per email verified.

If the email is valid, it’s added to your list. If it looks like there might be an error in the address or the address might be fraudulent, the service performing this audit will ask you if you want to continue with adding them to your list.

Identifying Illegitimate Emails Method 2: Long-Form Email List Cleansing

This method involves taking a large, pre-existing list and running it through a validation process. This goes through a number of actions, like looking up all the MX (mail exchanger) records for all of the domains of the emails to see if any are invalid and remove any emails from bad domains.

The validation process will also start an SMTP (simple mail transfer protocol) connection, which makes it look like they’re about to deliver an email to that address, but stop before it’s actually delivered. By doing this, the receiving ISP can tell you whether or not the email address exists at that location.

Again, we use BriteVerify to run our list through this validation process.

Between these two methods of email validation, both as part of sign up and before importing a new list, you’ll filter both non-existent email addresses and eliminate some (but not all) spam traps from your list.

Next is…

(NOTE: Want to make an email marketing campaign that can’t be ignored? Get your FREE email marketing guide from Maropost by DigitalMarketer and learn the strategies to get the most out of your email marketing — from what your emails should and shouldn’t do to the KPIs to pay attention to. Get your copy here.)

Advanced Email Deliverability Tactic 3: ISP Distribution

Now, this isn’t so much a tactic as it is a strategic piece of information.

Knowing the ISP distribution of your subscriber list won’t win you any deliverability points, but you can use this information to better understand your inbox placement and engagement. Maropost advanced email deliverability tactics

Different ISPs operate differently.

It sounds simple, but it’s not always something we consider when sending. What might be considered spammy content on one ISP might not raise any eyebrows on another.

The level of spam detection sophistication varies between ISPs, and while larger ISPs can afford to build their own reputation filtering systems, smaller ones have to outsource their reputation filtering systems.

It’s also important to know your distribution so you can calculate how your performance metrics…

  • Bounce rate
  • Complaint rates
  • Open rates
  • Click rates

…vary, if at all, between domains.

Now, if your metrics are skewed for one ISP, rather than spread evenly, there’s a different course of how to address it…

Let’s say your engagement rates are lower on Yahoo than other ISPs. In that case, you’d want to enact stricter rules for suppression lists and list cleansing specifically for Yahoo.

"It comes down to testing and seeing what works best for your campaigns."For instance, instead of removing inactive subscribers from your list after 90 days, on Yahoo you’d cleanse your list at 60 days (and start your win-back campaign 30 days earlier, too).

But remember, there’s no universal move to make for enacting stricter rules that would work for ALL senders.

Two senders both suppressing after 60 days might have to shorten the period by different times. It comes down to testing and seeing what works best for your campaigns.

But by establishing different rules for different ISPs, you can target problem areas in your deliverability.

The next tactic we’ll focus on can mean the difference between reaching users’ default inbox and landing in their promotions tab.

Advanced Email Deliverability Tactic 4: Treat Email as a Two-Way Communication Medium

With so much of our time as email marketers spent sending out emails, it’s easy to forget that email is meant to be a two-way communication medium. But keeping this in mind is an incredibly powerful way to increase deliverability.

One move to start that two-way communication is with user-level whitelisting. Maropost advanced email deliverability tactics

What is user-level whitelisting?

In its most basic form, it’s when a subscriber adds you to their address book. But it’s also a reputation metric ISPs use to make decisions about filtering emails, so it can mean the difference between reaching the default inbox and reaching the promotions tab.

However, being added to an individual’s address book isn’t the only way to gain the privileges of user-level whitelisting.

If enough people on your list have extended user-level whitelisting to your send address, ISPs will make a default inbox decision for everyone on your list. So, even if you only have a percentage of your list personally whitelist you, you can receive the benefits for your whole list

Just to clarify — whitelisting is not a magic wand. "Keeping this in mind is an incredibly powerful way to increase deliverability."

But the best practices to generate whitelisting include:

  • Low complaints
  • Good content and subject matter
  • Adding the senders from address to the end users contact list
  • Having Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) setup on the Domain Name System (DNS)
  • Speed volume and frequency of the email

You’ll know you’ve been whitelisted when:

  • Deliverability is at 100%
  • Open rates are around 15-30%
  • Click rates are at 5-10%
  • Complaint rates are under 0.1%

Other interactions to incorporate into your email marketing include having subscribers reply to your emails. While it’s not a campaign that’s spoken about a lot, a reply-to campaign can help upgrade your IP reputation.

Which brings us to our final tactic.

Advanced Email Deliverability Tactic 5: Segmentation by IP and Subdomain

Different kinds of mail have different levels of urgency, and more importantly, different levels of deliverability.

Maropost advanced email deliverability tacticsFor instance, some emails, like transactional mails, tend to have a high-level of urgency for subscribers. These are emails like receipts and password resets, and they typically see 8x higher opens and clicks. However, the send volume of these emails isn’t typically that high.

On the other hand, promotional emails are more important to marketers than they are to subscribers. For these emails, a mere 20% open rate is considered to be a success.

With engagement filtering, if you have a little bit of transactional email mixed in with a whole lot of promotional email, then it’s possible for promotional email to cause ISPs to bulk or block your content, hurting the deliverability of your transactional emails.

Why is this?

Because engagement is lower on promotional emails, they can detract from your sender reputation (which depends heavily on engagement levels).

A lower sender reputation means lower deliverability. Lower deliverability means lower deliverability on all your emails.

Unless… you send from different IPs and subdomains. In that case, the sender reputation on one will not impact the sender reputation of the other.

So, how do you send both emails without the deliverability of one hurting the other?

The answer is to keep them separated, by sending transactional emails from one IP and subdomain and promotional emails from another IP and subdomain.

If you use different IPs and subdomains for different email types, you won’t risk the deliverability of one due to the engagement levels of another. So, even if your open rates on promotional emails dip, you’ll know that subscribers will be able to receive those urgent transactional emails without a problem.

After you’ve employed all these methods, how will you know your efforts are paying off?

How to Know the Advanced Email Deliverability Tactics Are Working

Here are a few key performance indicators (KPIs) you can look to see change when employing these advanced email deliverability tactics.

Graphic showing bounce rate, complaint rate, and open rates

Bounce Rate

Your bounce rate will go down.

With better email verification processes in place, fewer invalid addresses will be on your list, meaning you’ll have fewer bounces.

Complaint Rate

Your complaint rate will go down.

By using suppression lists and list cleansing, fewer uninterested subscribers will be receiving your emails. When your most engaged subscribers are the ones you keep, you’ll know that the people getting your emails actually want to be receiving them.

Open Rate

Your open rates will go up.

However, this improvement comes with a caveat.

While you should want to improve your open rates, you don’t want to sacrifice too much of your open volume. And as much as we encourage clients to keep a clean, lean list, there is such a thing as too lean a list.

Too lean of a list will depend on the sender and how they use email marketing. For some, a list of 10k after cleansing is still huge, for others a list of 10k after cleansing is miniscule.

Improving email deliverability is all about balance. Use these five advanced email deliverability tactics to balance your list size and boost your deliverability without sacrificing your audience size.

(NOTE: Want to make an email marketing campaign that can’t be ignored? Get your FREE email marketing guide from Maropost by DigitalMarketer and learn the strategies to get the most out of your email marketing — from what your emails should and shouldn’t do to the KPIs to pay attention to. Get your copy here.)

Tim Starr

Tim Starr

Tim Starr has been Maropost's Senior Director of Deliverability for more than 3 years, and has worked in Deliverability at more ESPs than anyone else, starting in the field back in 2003 before it was called "Deliverability." His previous gigs include Sendgrid, Marketo, and Responsys (now Oracle Marketing Cloud). Tim was born and raised in the San Francisco Bay Area but escaped to Colorado in 2012. Tim's hobbies include martial arts, military history, and politics.

Subscribe to the DM Insider Newsletter

Subscribe to our weekly newsletter that delivers the most actionable, tactical, and timely marketing tips you actually need in 7 minutes or less. Get an edge over the competition, for free.