Email deliverability, or the likelihood of your brand’s emails successfully landing in a subscriber’s inbox, is a complex issue.

There are a web of different factors that play into whether or not your brand's promotional email messages reach their intended targets, which you already know if you’ve read our prior post on email deliverability. However, there are always more nuances to understand when it comes to how to best optimize your email campaigns to boost your chances of getting your messages successfully delivered.

Before getting into the finer details, let’s review the basics.

What contributes to deliverability?

1. Sender Reputation

Your sender reputation, IP score, or sender score, is a score from 1-100 that’s assigned to you to rank how legitimate of a sender you are. ISP’s use this score to determine your credibility.

If you have a high sender score, your content is more likely to reach your recipients’ inboxes. Senders with low scores will have issues getting their messages successfully delivered and are more likely to get their emails marked as spam.

Here are some signals that are used to compute your sender reputation.

  • Spam Complaints
  • Hard and Soft Bounces
  • Sending Volume Trends
  • Content Quality

2. List Hygiene

Cleaning your email list is a standard practice that can help your email deliverability.

List cleaning starts with identifying subscribers who have gone cold on you. These cold, or disengaged recipients aren’t taking any actions, including opening, clicking, or subscribing.

You’ll want to remove disengaged subscribers from your list. Not only do these recipients detract from your deliverability and sender reputation, but they also incur unnecessary costs, given that your ESP is still charging you to keep these individuals on your list.

Another phase of list cleaning is working to reengage subscribers who are salvageable. To do so, you can send a warm-up sequence to recapture their attention. In a warm-up sequence, you aim to re-establish a connection with recipients by reminding them of the value of your communications as well as the benefits your product or service provides.

This process of list cleaning will directly benefit deliverability by boosting overall engagement metrics.

3. Email Volume and IP Warming

Mastering email volume is key in showing ISP’s that you’re a good sender.

Warming your IP is a best practice if you’ve recently started using a dedicated IP address, or if you haven’t sent for over a month. IP warming helps you establish your reputation as a legitimate sender and avoid getting your messages mistaken for spam.

The practice of IP warming involves gradually increasing your email volume over time.

If you randomly start sending high volumes of email from a cold IP, ISP’s will see this as a red flag, given that volume is a signal that they monitor to detect spam. As such, you should start sending at a low or moderate frequency and increase volume over time.

4. Message Frequency

When it comes to mastering your email frequency, consistency is key. ISP’s see view a consistent email cadence as a positive signal. Your optimal sending frequency will depend on your industry and the types of alerts you typically send via email. For example, if you’re an eCommerce brand, you may send deals more frequently than you would as a SaaS brand.

No matter what industry you’re in, you’ll want to test what sending frequency works best in order to boost engagement. Once you’ve established a cadence that works well for your subscribers, you’ll want to maintain that frequency to continue building trust with the ISP’s to ensure better deliverability over time.

Aside from these overarching themes, you’ll also want to zero in on some specific ways you can optimize your emails to improve deliverability. Let’s get into it!

6 Email Optimization Tips to Improve Deliverability

1. Consider Content Structure

The most important determinant of email deliverability is engagement. One of the most effective ways to boost engagement is to create content that’s both visually compelling and valuable to your recipients.

You should start with an enticing subject line that will prompt recipients to open your messages. Your subject line should also accurately reflect the content readers can expect in your email body. Matching your subject line with your email body content will contribute to your reputation as a good sender.

Content structure also affects how ISP’s and recipients process your emails. You’ll want to ensure you’re using a responsive email design to make viewing easy on subscribers.

When you structure your emails, you should also be thinking about content hierarchy, or the strategic ordering of content from most to least important. Organize your content so that your emails will be easier to read and digest, which will make them more engaging and give readers a reason to open your next promotional message. Simplifying your message is often an excellent tactic for improving readability and a general email marketing best practice you should adhere to.

You should already know that including an unsubscribe link is not just polite, but legally required for email compliance. It might be easy to overlook how your unsubscribe link’s design — including its position and visibility— might affect recipients’ ability to opt out. However, if your unsubscribe link is too hidden, whether this is intentional or unintentional, your recipients might just mark you as spam. If too many recipients mark you as spam, your emails could increasingly get lost in spam folders or bounce, tanking your deliverability.

3. Balance Images and Text

If you use too many different colors, fonts, and images, this too can negatively impact your deliverability. Generally speaking, your image-to-text ratio should be about 60 to 40 percent. The more images you include, the higher the chances that filters will see your content as spammy. You should also be thinking about how your recipients are perceiving your email content. Adding unsupported fonts and colors can lead your emails to be unreadable or to appear differently to recipients who are on certain ISP’s. To avoid this outcome, you should reference updated lists of supported email fonts and colors to make sure your recipients will be able to read and appreciate what you send.

4. Avoid Spam Trigger Words:

Email providers are just out to protect their recipients. To do so, these algorithms react to words or phrases that are typically fraudulent and risks sending these emails to the spam folder.

Spam trigger words alone aren’t enough to banish an email to a recipient's spam folder, so if you’re adhering to the other best practices we’ve mentioned, you’re less likely to be at risk if you do decide to include some of this language.

Just be wary that the following are dangerous copywriting practices to use if you want to avoid being flagged for spam trigger words.

  • over-sensationalized copy
  • exaggerated or clickbaity language
  • Forceful or aggressive language

Let’s get into some common examples of spam trigger words.

“Near you”

“Be your own boss”

“Earn extra cash”

“Expect to earn”

“Double your”




“F r e e”


These are just some select examples, but you can easily research more exhaustive industry-specific lists of spam trigger words. Some words on these lists may be hard to avoid 100 percent of the time in effectively communicating your message, so remember you can always 1) use them sparingly and in context 2) use synonyms or alternate phrasing, or 3) link out to a longer form message within the email.

5. Include Image Alt Text

Alt text is a short line of text displayed when subscribers cannot access the images in your emails. Including effective alt text in your emails can boost deliverability by making your emails more accessible and engaging even when subscribers can’t see your images.

Alt text is useful for visually impaired subscribers who are using a screen-reader. Without this descriptive text, your emails will be inaccessible to these subscribers.

Using alt text can also be informative for subscribers who have images blocked or turned off. Many email clients and users disable images by default.

In either of the prior scenarios, alt text can help properly communicate your email’s content to readers even without the full visual experience.

6. Stay On Brand

Staying true to your brand will contribute to better deliverability because it makes your content more recognizable and more credible.

With that in mind, you should prioritize brand consistency by maintaining brand elements such as email send name (which should clearly include your company name), your copywriting style, your footer, and more.

Make sure your subject line echoes your brand voice and that it doesn’t sound click-baity. Enhance your emails with your brand colors, imagery, and graphics without pushing the image-to-text ratio out of balance.

Finally, stay on brand by making sure your content structure and density is similar to other long-form content your brand produces. Creating a uniform brand experience will improve engagement, which in turn will boost deliverability.

7. Reduce Bounces

Bounces typically occur for a variety of reasons. Sometimes, you're sending emails to addresses that do not exist, have full inboxes, or have server outages. Other scenarios include that you're sending from a domain with a poor sender reputation or your message content itself could be flagged.

To maintain a healthy email program, it's recommended that you keep your bounce rate under 5 percent.

Here are some key ways you can reduce your bounce rates:

Perform Email Authentication

Email authentication usually involves sending a verification email to your user's provided address, after which the user can click a link to verify the email is valid. This prevents the user from providing an incorrect email address they don't use or own. Once validated, it is then best to pass to OneSignal.

For optimal deliverability, you should only send messages to recipients who have knowingly signed up to receive your emails. Just because a user gives you their email to sign into your app, they don't necessarily acknowledge that they want emails from you. However, you can instead use a prompt to ask the given user what kind of emails they want and set tags to later serve them the content they've consented to receive.

Email Validation & Suppressions

If you already have a list of emails and want to validate them, ESPs like Mailgun and SendGrid provide email validation tools that you can use to check a list before uploading to your messaging provider.

Back to the Email Basics

Who are the Key Players in the Email Game?

In case you need a recap, here's a quick summary of the different parties involved in the sending of an email from your business to its intended recipient.

Email Senders

The first party involved in the journey of an email is your business or the email sender. Depending on your strategy you might be looking to reach your subscriber list with transactional reminders like passwords confirmations, shipping information, or receipts. You could also be sending marketing messages such as LTO’s, promotions, cross-sells, and more. Your priority as a sender is to maximize your deliverability and reach your customers more consistently, aiming for higher open and engagement rates.

Email Service Providers

You probably have heard of Email Service Providers, or ESP’s, which are third-party services that provide marketing and bulk email services to their subscribers. On a basic level, ESPs store and send emails, but they can also provide features like email and marketing automation, dynamic content, and segmentation. Learn how to choose the best email service provider for your needs.


Gateways are another party that that make it possible for you to send an email. Email gateways include Internet Service Providers (ISP’s) and other entities that control whether your email reaches its desired recipient. Examples of these providers are Gmail, Yahoo, Outlook, and Hotmail. They create a safe space for recipients to receive emails by performing actions such as scanning content, filtering spam, and preventing phishing. Email gateways' key goal is to protect recipients from spammers.

What's important to note is that if you can achieve deliverability with major ISP’s, you’ll likely satisfy the smaller ones, given that smaller providers mimic the algorithms used by major ISP’s. Other gateways include anti-spam systems and blacklisting orgs.


Finally, the most important player in this email game is the recipient. You might already know that your recipients are your opted in customers, who ideally receive, open, and/or engage with your content. Your recipients are the targets of your email campaigns.

The Journey of an Email

Assuming you now understand the parties involved in an email's trajectory, When shoot of your message, your email first passes through internal filters before traveling the interwebs and arriving at an inbox server. Here, the email must pass ISP checks and filters. Then, the email is sorted by internal spam filters into a recipient's spam or inbox. Finally, once a message is successfully delivered, its fate lands in your recipients’ hands. Whether they positively or negatively interact with the content is up to them.

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