The Best Email Deliverability Guide for Marketing. Ever.

Email deliverability: It's the cornerstone of good email marketing strategy and planning. Not sure why? Our guide will make you an expert.
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Email Deliverability Guide Part 1: Mission Inbox-able

Email deliverability (aka inbox deliverability) isn’t yet a buzzword on the lips of every digital marketer out there. But it needs to be. Think about it. You work hard on your email marketing programs. All that work is wasted if your emails never make it to the inbox to fulfill their destiny. That’s why the best deliverability service team in the business came together to write this, The Best Email Marketing Deliverability Guide. Ever. Read on for chapter one.

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Email deliverability is worth careful strategy and study if you don’t want other elements of your email strategy to suffer.

Email Deliverability: What is it, anyway?

In simplest terms, deliverability is the overall health of a sender’s email program. You might have read online that deliverability is all about hitting the inbox. True: that’s the end goal.

But Delivery Rate is just one aspect of a holistic approach to email deliverability. Focusing only on delivery rate omits important aspects of your email program that contribute to your overall health and reputation as a sender. 

A holistic approach to deliverability takes more than delivery rate into account. Before diving in, make sure you’re familiar with these common email marketing and deliverability terms. 


A process that confirms to ISPs that you are who you say you are, and that your marketing automation platform is sending on your behalf. Common authentication methods include DMARC, SPF and DKIM


An email that cannot be delivered to the recipient’s email server.

Hard Bounce

An email that bounces because the address does not exist.

Soft Bounce

An email that bounces back for reasons other than a hard bounce (e.g., due to a full inbox or server outage). Soft bounces are often temporary, and senders can typically fix them. 

Click Rate

Number of clicks divided by number of emails delivered.

Click-Through Rate (aka Click-to-Open Rate)

Number of clicks divided by number of emails opened.

Data Hygiene

The overall quality of your email list and the associated data. Effective email strategy, and strong deliverability, always rests on a foundation of high quality lists with the right information

Delivery Rate

The percentage of emails that are delivered. Calculate it by dividing the number of emails delivered (total emails minus bounces) by the total number of emails sent.

Email Channel Health

Metrics like engagement, conversions, and even the ROI of your email program. You may be saying, “Isn’t that email strategy, not deliverability?” And you’re hitting on just the point we’re trying to make: you can’t separate solid email strategy from strong deliverability. And you shouldn’t try. 

Inbox Rate

The percentage of emails that are delivered to a non-SPAM folder. It can be estimated, but as a sender, you’ll never know the exact inbox rate.

Open Rate

Number of emails opened divided by number of emails delivered. 

Inbox Delivery: A Mystery Wrapped in an Enigma

Let’s start with a scene. A marketer walks into Act-On (or, more likely, joins us on Zoom) and meets with our Deliverability Team. They’re understandably eager to get started. They kick things off with what should be a simple question: 

“What is my inbox rate?”

The Deliverability Team hesitates, knowing their answer is going to disappoint the marketer a little. They reply:

“We can narrow it down to a relatively tight estimate…but it will always be a mystery.”

The marketer looks confused. How can this be? They came here to get answers!

Well, today’s inbox is not what it used to be. For starters, what do you consider the inbox? The major ISPs (Inbox Service Providers such as Gmail, Yahoo! and Microsoft) all have their own way of filtering incoming emails according to the user’s expectations and customizations. 

For instance, Google has its customizable tab system that includes categories like Inbox, Social, Updates and Promotions. Microsoft uses its own tab system divided into Focused Inbox, Promotions, Social, and Other. And of course, most major platforms offer users customization options to filter and route emails to their own subfolders.

Further, the ISPs use their own “bucketing” systems based on recipient behavior to route emails. These systems are opaque from a sender’s point of view–you can’t see what’s going on behind the curtain. A different message to the same group from the same sender, based upon content and reputation at the time of sending, might have a totally different placement.

As a sender, you don’t have visibility into any of this activity. You’ll only know whether your email was accepted or not. If an email is accepted, you can’t know whether it hit the “Inbox,” or a “Clutter” or “Promotions” folder where it’s less likely to be opened.  

Find the right tools to help with inbox delivery

Fortunately, there are tools available to give additional insight into the inbox—Act-On’s Deliverability team uses Inbox Monster, which provides reasonably accurate representations of the inbox.

 For customers enrolled in Act-On’s Enhanced Deliverability Services, we tailor a 250ok list to get an idea of the inbox landscape and to provide guidance on improvements. Other tools include Glock Apps and Return Path, to name a few. But all of these apps come with a hefty caveat: their information is an educated guess, and not guaranteed to be accurate.

Optimize and test for mobile 

Roughly half of all emails are opened on mobile. Making sure a send is renderable on both computer and mobile is a necessity. Not only that, but many inboxes are configured completely differently on mobile devices compared to desktop. Often, ISPs will route an email directly to spam if it isn’t rendered properly on mobile. Avoid poor performance on mobile devices by using your marketing automation platform’s mobile preview feature to check how your email looks and reads on mobile devices. 

Sender reputation and email marketing deliverability

When you have a good sender’s reputation, your messages are more likely to hit the inbox. Likewise, a bad reputation will make emails bounce or hit the SPAM folder at a higher rate.  Each ISP and filtering company puts different weight on different factors to determine a sender’s reputation. 

Reputations can often be found on the postmaster page of the major ISPs. For instance, Google’s postmaster site rates domains on a 4-tier scale: bad, low, medium, high. Other ISPs have different scales and different reasons for affecting reputation. 

A good reputation is paramount to a sender, as it can help compensate for any deliverability issues that arise. It also leads to a higher ROI for emails. Good reputation is based on hard work, adherence to best practices, and versatility in a changing landscape. Data quality will have the largest impact on your reputation, followed by maintaining an engaged audience.

Sender Reputation Factors
How they impact you, and whether you can see them
Visible to Sender/Negative ImpactVisible to Sender/Positive Impact
-Spam complaint (at most major providers)
-Hard bounce
-Soft bounce (from reputation)
-Repeated emails to unengaged recipient
-Unauthenticated sends
-Unformatted/unrenderable content
-Hidden links
-Bad or blocklisted links
-Unsecured links
-Authenticated sends
Double opt-in confirmation
Hidden from Sender/Negative ImpactHidden from Sender/Positive Impact
-Sending to a spam trap
-Deleted messages
-Ignored messages
-Email views less than 1 second
-User reports as abusive or phishing
-Spammy content
-User hitting the “This is spam” button (Gmail and most B2B domains)
-Email views greater than 1 second
-User creates folder for email
-Email promoted to better folder (e.g., Promotions to Inbox)
-Moving a message from SPAM
-Adding sender to address book
-Starring/marking as important

Fixing your bad email sender reputation

Repairing a reputation requires tight control of all email sends and more granular oversight. This is your chance to convince the ISP that you’re following best practices, and that your messages are useful for your audience. Keep these tips in mind if you find yourself with a damaged reputation in need of repair.

  1. Use only the very best data. Maybe this means that pile of leads from the trade show you just attended has to wait. But it’s better to wait until the repair is complete and your reputation is back on track than send to those untested leads right now.
  2. Shorten your engagement segmentation period by one-third to one-half. Only email those who are actively engaging with your messages. You’ll likely need to sunset many emails during the repair.
  3. Perform list hygiene. We’ll cover this in detail in Part 2. In short, you’ll need to perform both third-party list hygiene and sunsetting on your unengaged contacts to ensure data integrity.    

Once reputation repair is complete, you’ll need to continue to follow best practices to avoid your reputation slipping. ISPs have long memories; with each reputation hit, it becomes a little more difficult to repair.

Performing a hard reset of your email program

A hard reset is exactly what it sounds like: the marketer stops sending any emails from the affected domain/IP for a minimum of 30 days. This might seem extreme, and it can be extremely difficult to convince stakeholders at your organization. But desperate times call for desperate measures. (One reason we recommend that marketers maintain separate traffic streams for different types of emails on different domains: this way not all company email activity has to stop in the event of a reset or reputation repair).

Once the sending has been paused for the requisite 30 days, sending can resume with the following strict setup:

Maintaining a good reputation is absolutely critical to ensuring inbox placement and avoiding the spam folder. While a bad reputation can be repaired, you should always follow best practices, maintain quality data, and keep your audience engaged to prevent damaging your reputation in the first place.

Email Deliverability Guide Part 2: Strategy

We always recommend that email marketers consider deliverability as a core element of their email strategy, not an afterthought. Remember that in Part 1 we discussed how engagement, performance, and overall channel health make a significant impact on deliverability. Addressing all the above elements in a comprehensive email marketing strategy will save endless time and frustration down the line. Sending one-off emails without fitting them into a strategic framework is a recipe not just for low performing emails, but for getting your content flagged as SPAM.

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Going back to the drawing board isn’t necessary if you factor email deliverability into your strategy from the start.

Segmentation: A strategy & deliverability two for one

Ensuring your email is sent to the right audience is extremely important for deliverability and engagement. Without proper audience targeting, you risk wasting resources and dinging your reputation as a sender. 

Of course, you’ll always have some necessarily broad emails to groups of contacts you haven’t learned much about yet. But these should be minimal compared to more targeted sends. Whenever possible, you should send emails to targeted segments who you’ve learned something about through your nurture efforts or lead gen campaigns. 

Segmenting by position level in the organization

We recommend segmenting by position level. Grouping your contacts based on their role within an organization will empower you to provide more relevant content and resources to assist them throughout the buying process. Collect this information via form fills and update your CRM to help your segmentation efforts.

Segmenting by funnel/journey stage

Another smart segmentation strategy. Matching the content to their stage in the customer journey means your messages will be more relevant and persuasive. Near the top of the funnel, it’s more likely that you’ll receive opt outs. That’s okay! This is how the process should work. In a way, those contacts are doing you a favor by letting you know your marketing isn’t relevant to them. Find ways to learn more about your customers at this stage (e.g., interactive surveys) to aid your targeting efforts as they move down funnel. You’ll likely see fewer SPAM complaints for mid and bottom funnel contacts.

Finally, consider segmenting by engagement level. Segmenting your data is always important because it allows you to target the right people. But segmenting based on engagement is even more important for maintaining a good sender reputation.

Due to the individual nature of each sender’s engaged group, it is critical to define engagement for each sender. An engaged individual has taken some predefined action within a certain timeframe, such as clicking through to a piece of content. Your email marketing strategy should define the actions that point to an intent to buy based on previous closed/won deals.

Balancing deliverability and email timing

When and how often to send email is a key part of your strategy, and can have unforeseen consequences for your deliverability efforts. Consider the factors below when scheduling out your campaigns: 

Email volume

Your email volume can have a drastic effect on deliverability and reputation. High volumes require a good reputation, lower volumes less so. Best-in-class senders can get away with sending millions of emails in under 20 minutes, whereas a low reputation sender may struggle to get 20,000 emails accepted and delivered to the inbox in 3 hours.

It’s also important to keep your sends consistent. Intermittent and erratic email volumes can tank your reputation and deliverability; consistent sending can bolster it. ISPs want to see consistent sending without dramatic spikes or plummets week-to-week. At most, you can increase consistency by 2 to 2.5 times before it begins to impact your deliverability. 

To increase your volume without dinging your reputation, plan a slow, steady ramp up in volume. Start with a very low sending volume. A weekly doubling of volume is a good rule of thumb for most ISPs. If you run into issues, pause your efforts at the previous volume until the issue is resolved or a week has passed.

Email cadence

The cadence, or the frequency a sender wants a recipient to receive emails, should be a part of your overall email marketing strategy. Unsure how to determine the best cadence for your customers? The frequency of emails should be informed by the sales cycle of your product. For example, if you have a 9-month sales cycle, a weekly email cadence is too frequent for your average customer. 

Top- and middle-of- funnel recipients and current customer emails should be spaced out to avoid fatigue. In contrast, bottom-of-funnel prospects and newly onboarded customers (including active renewals) demand a higher cadence of emails to support and inform.

Email Fatigue

We’ve all been there: you sign up to receive emails from a potential vendor because you’re curious about a product, only to be inundated with all-too-frequent emails. It’s sort of the email marketing equivalent of agreeing to go out for coffee only to show up and find your date on bended knee with an engagement ring in hand. To avoid the SPAM reports and disengaged recipients that can result from email fatigue, devise a strategy for who you target and how you target them.

Fortunately, marketing automation offers tools for managing and preventing email fatigue. Act-On allows users to set up email fatigue suppression rules to ensure that no single prospect receives more than your optimal number of emails within the timeframe that you define. You can also set up your automated programs to have waiting steps designed to lessen the number of emails received. By controlling your cadence based on user action, a program can be sped up or slowed down.

Data cleanup and sunsetting emails

It’s important to remove (i.e., sunset) unengaged recipients from your programs at some point. Your sending cadence and level of contact should determine when you choose to sunset these emails. A prospect who is unengaged should be treated differently than a hand-raiser or a current customer. Reducing the number of opt outs, hard bounces, and unengaged recipients from email lists helps your automated email programs run faster.

Unengaged recipients drag down your stats and lower your reputation with every email without an action. Worse, they can also be a source of spam traps.

Email Deliverability Guide Part 3: Content

Developing and distributing relevant, compelling emails won’t do you any good if they all end up in the SPAM folder. On the flip side, emails that get delivered successfully won’t help engage your prospects and move them down the funnel if the content is lacking. Good email content needs to be optimized for deliverability and content best practices

As a rule, any portion of an email can get you blocked or reported as SPAM. To make optimizing content more manageable, we’ve broken this chapter down into two separate sections: the first focused on optimizing for engagement (which improves sender reputation over time), the second focused on optimizing for inbox placement.  

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Send your key metrics up and to the right with content that maximizes your deliverability results.

Content that determines engagement

The connection between open rates and deliverability should be obvious by now: ISPs consider an opened email the sign of an engaged recipient, which has positive impact on your deliverability. But click-through rates for your email content also contribute to your deliverability for the same reason. Recipients clicking through the CTAs in your email might not be relevant to inbox placement immediately, but it has a cumulative effect over time, as ISPs consider it engagement signal. (Learn more about how to re-engage disengaged recipients).

For engagement and deliverability, the top three lines of an email are the most important: the “From” line, the subject line, and the preview text. We’ll also discuss CTAs in this section.

“From” addresses and display names matter

The “From” address can have a huge impact on deliverability and engagement. Upwards of 40% of recipients decide whether or not to report something as SPAM based on the “From” address alone! We suspect that statistic has a lot to do with companies and employees becoming more savvy about increased hacking and phishing attacks around the web. With a more educated audience, it’s more important than ever to establish trust from the start, and that means the “From” line.

Similarly, spammers often try to trick their recipients with deceptive display names and mismatches between the display name and the email. (For example, using someone famous in the display name, like Warren Buffett, when the email address is something completely unrelated). For this reason, display names are very important for deliverability.

Follow these fundamental rules and best practices when configuring your display names and “From” lines:

Avoid using “noreply@” in the display name

You should always send from an email that someone can reply to, even if the response is forwarded to another company email. ISPs check for this when scanning email, and if the reply-to link is broken, it may affect inbox placement. Further, even if your message lands in the inbox, using a “noreply@” address can discourage engagement. Send from an email that motivates your target audience to open and read your message.

Don’t use generic addresses (e.g., postmaster@, admin@) 

These addresses have specific meanings in the world of email and the internet, which means they should never be used for marketing and sales purposes. (For the same reason, senders should also avoid sending to these addresses). 

Let’s say your from address is “[email protected],” and the display name is “CEO of Skynet.” That’s a mismatch. If the email address and the display name don’t jibe, it’s a signal to the ISP that something phishy might be going on (pun intended).

Only use a personal display name once you’ve formed a relationship 

Although emails that have a personal email as the display name typically have slightly higher open rates, misleading an email recipient can have deliverabiliy consequences. Use more broad and general display names at first. (Think, “New Customer Team” or “Skynet Marketing.”) Later, you can introduce a specific person who will be emailing, and transition to emailing “as” them. (e.g., Arnold Schwarzenegger / [email protected]).

Clarify the sender when using broad email addresses 

“Marketing” is an ineffective display name because nobody knows exactly who that is. Instead of using an email address that is hard to identify, use your display name as an opportunity to stand out and define your brand. 

Avoid deceptive display names

Whatever you do, don’t use a misleading display name. ISPs see that as a spammer signal. Think of all the emails you’ve avoided opening with display names like Crown Prince of Zamunda.

Use proper capitalization

Always follow the same capitalization format when writing your display name. Improper capitalization sticks out like a sore thumb and throws up red flags to SPAM detectors.

Do not use emoji in a display name

There’s a place for emoji in email marketing (often, the subject line). It’s not the display name. Keep it professional when identifying yourself.

Subject lines and email deliverability

Email marketers have some idea of how to craft engaging and motivating subject lines, but there’s always more to learn and new ideas to try. Think about it too long, and the challenge can seem daunting: you only have a few words to capture your audience’s attention, but you also have to avoid red flags and misleading words that can trigger the ISPs’ SPAM scanners. 

For deliverability, it’s all about setting expectations and staying consistent. The subject line should set up the email to follow; if they’re too unrelated, you can send recipients bouncing back out of your message. Of course, from a content perspective, you want subject lines to be somewhat unexpected. If it’s the same thing they’ve seen over and over, your line is unlikely to break through and inspire action. Balancing these competing demands can be challenging. Follow these Dos and Don’ts along the way to ensure you don’t negatively impact deliverability as you pursue subject line excellence.

Clearly state why to open an email
Check out this month’s promotional pricing 
Mislead readers to trick them into opening
If you don’t buy, you’ll regret everything!
Use urgency with specifics
Conference registration ends Friday!
Use urgency without explanation
Hurry! Last chance, don’t miss it!
Use correct capitalization
Tips for optimizing SEO on your website
Use ALL caps or no caps
Use emoji sparingly
Happy birthday! 🎂 We value your business!
Use emoji throughout the subject line
🥳🥳🥳Save 💸💸💸on 💻for your🎂🥳🥳
Personalize the subject line to make it personal
Tiffany, seen our new blog on dental hygiene?
Personalize using confidential or sensitive information
Tiffany, happy with your gum transplant?

Preview text and inbox delivery

The final thing recipients see before deciding whether to open an email is the preview or first line text…if they actually see it, that is. Ultimately, the ISP and their platform determine which information to display. For instance, some ESPs always show the first line of the body copy of your email, even if you’ve provided specific preview text. Certain apps show as many characters as a reader’s screen and settings will allow but some limit preview text lines to as few as 40 characters. 

There are a few mistakes related to the first line of email that senders commonly make.

When crafting your preview text, make sure to avoid the following:

  • Information About Website View Mode: Trouble Viewing? View online
  • Improperly formatted HTML Code: <div {style=”display: none; max-height
  • Alt-Text for Image or Banners: [Banner][Banner][Banner][Banner]
  • Addresses or Other Location Info: 1600 Pennsylvania Ave, Washington D.C.

Calls to action (CTAs) and email deliverability

Clicks on your CTAs improve deliverability in the long run because nearly every ISP interprets clicks as positive engagement. The CTA is the most important link in your email: it can make a huge difference in recipient engagement levels, even in the case of similarly designed emails. These best practices will help you craft CTAs that get seen and clicked to drive conversions:

Make your CTA separate and distinct

The most common way to make CTAs stand out is to include a button that is centered and separate from other text within the body of the email. Part of the reason this method is so common is that it is the easiest way to enhance your CTA and motivate readers to click.

If a button does not seem like the most appropriate choice for your email, you can embed your CTA within the text, but make sure to use elements like color and phrasing so the CTA stands out.

Avoid images for CTAs

In our experience, image-based CTAs cause confusion. Recipients either don’t expect the image to be clickable, leading to depressed click-rates; or, they accidentally click on the image, leading to falsely inflated click-rates. In the latter case, this can often lead to an increase in SPAM complaints if recipients feel they were misled. 

Choose a single primary CTA

Though an email may have multiple CTAs, it should always have one primary CTA that stands out from the rest. If you do include multiple CTAs, make sure it’s clear where users need to click, and what they’ll be clicking through to. Your main CTA should draw the reader in and serve as the focal point for the entire email. 

Content that gets marked as spam

Most of the elements discussed in this section don’t directly affect engagement, but they can affect inbox placement. Many senders fail to pay attention to these important elements, which can create deliverability problems for an otherwise quality sender.

Alt-Text and email deliverability

Every image in your email should have alt-text. Alt-text is an important accessibility feature for the visually-impaired. But it’s more than that; lack of alt-text can increase the probability of your email being marked as spam. Google and other ISPs check alt-text to make sure it matches the content of an image. For the best alt-text, use concise, accurate language to describe the image’s content. Descriptive is the watchword here: don’t try to stuff the alt text with keywords or marketing messages. There’s a time and place for that. 

Links and URLs in emails are one of the most scrutinized elements of an email by spam filters. Malicious actors often use links to external websites for malware attacks and phishing for personal information. Additionally, the reputation of the domains you link to in your emails is a major indicator of whether the email is spam or legitimate. For these reasons, we recommend following these best practices when dealing with links in emails:

  • Always use HTTPS for all your linked URLs:
    Linking to secured websites with SSL certificates improves trustworthiness and the likelihood of inbox delivery. ISPs routinely place emails with unsecured links in the spam folder due to the number of data breaches on the web.
  • Don’t link to blocklisted third party sites:
    If you link to a domain that’s on a spam blocklist, your email will likely bounce or be placed in a spam folder, regardless of your email reputation. (Protip: Act-On’s customers can use the built-in link validation tool of the Act-On platform to test their links). 
  • Avoid URL shorteners:
    Using a URL shortener is one of the best ways to secure a one-way ticket to the SPAM folder. ISPs distrust shortened URL links because they’re an easy way for phishers and spammers to hide their true destination. (In fact, Gmail doesn’t even trust emails that contain links from Google’s own URL shortening tool!) Avoid shortened URLs altogether. 
  • Make links clear and easy to identify:
    Emphasize link text using the industry standard practices: a text color visibly different from surrounding text, and underlining. Also, make sure recipients can see the underlying URL when they hover over the link. Malicious senders love to trick users by hiding links where they’re least expected, and pointing them to dangerous or unsecured sites. 

HTML and email deliverability 

Many spam emails have sloppy HTML or include additional formatting, often used to hide misleading content, such as links that recipients can mistakenly click. As a result, ISPs and spam filters consider messy or unnecessarily complex HTML as a red flag for SPAM. Messy code can also increase the size of your email, causing long loading times, which can also get your email rejected. Avoid these worst practices:

  • Font color similar to background color
  • Embedded Javascript
  • Extra large font sizes
  • An invalid font face
  • Non-standard ASCII characters
  • Bad tags or too many closing tags
  • iFrame in HTML
  • Including attachments within the HTML

Words/phrases to avoid for email deliverability

ISPs and major spam filters process and scan the content of hundreds of billions of emails each year. They know which word combinations are typical of spam emails, and if your email includes these phrases, your deliverability prospects are not good.

Avoid these words and phrases typical of SPAM: 

  • Free
  • 100%
  • Try now, buy later
  • Save
  • Last chance offer

Copyrighted images and email deliverability

Improper copyright usage complaints can be sent to anyone in an email transfer chain — including ISPs, data centers, filtering companies, and blacklists. Any of these agencies can take action to shut down emails with claimed copyright infringement violations.

The simplest way to avoid this is to make sure you either own or have permission to use the images in your emails and landing pages. If you’re using public open sourced images, make sure they’re also hosted on the open source site where they originated from.

Privacy policies and email deliverability 

Make sure all domains referenced in your email have a privacy policy on the domain website. Much like with SSL and link shorteners, a privacy policy is a requirement in the evolving world of deliverability. Many jurisdictions now require a privacy policy for websites that offer or sell any service, even if there is no ecommerce platform on the site itself. ISPs have followed suit and check links for privacy policies as part of the inboxing equation.

Did our email deliverability guide deliver, or do you need more information?

We’ve covered a lot of information here, but deliverability, and maintaining a strong reputation as a sender, is literally a full-time job for email marketing professionals. Continually testing and optimizing your email marketing is the only way to ensure that deliverability, engagement, and other positive results continue to grow. Maintaining good list and email hygiene is key to ensuring your emails get seen and that you are targeting individuals who want to engage with your content.

To discuss your own deliverability concerns, and see how Act-On can help you with your sender reputation, get in touch with the best email deliverability service team.

(Current Act-On customers can reach out to their customer success team at any time for assistance.)

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