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The Ultimate Guide to Email Deliverability

Email Deliverability Guide

Email marketing offers great possibilities to be creative when reaching your customers (or potential customers).

But before you can improve your customer’s experience through your top-notch email strategy, your email actually needs to land in their inbox.

Unfortunately, for 90% of the companies out there, it’s easier said than done.

But don’t pull out that tissue-box just yet. In this ultimate guide, we’ll go through the most common obstacles and topics that are connected with email deliverability.

We cover the topic of email deliverability in three major chapters:

Let’s start with the first one, the gatekeeper of all the emails you send…Internet Service Provider.

ISP blocking

Internet Service Provider Blocking

The different emails service providers (Gmail, AOL, yahoo, etc…) have various tools that filter the emails in order to get rid of unwanted messages. If your IP or domain smells fishy to them, it gets blocked!

However, it’s really easy to pass this blockade; all you have to do is to keep your email list clean and follow certain well-known rules.


Ending up on a blacklist is the result of sending too many emails people don’t want to read. Some blacklists only last for a day or two. Other custom blacklists have longer bans.

If you’re on a blacklist, contact the list owner as soon as possible. Responsible blacklist owners like to see initiative.

Of course, the best strategy is prevention. Avoid being blacklisted. There are numerous ways how you can fall onto the dreaded list-of-death. But as long as you follow the rules, you can make a good “FIST” of email deliverability.


This little acronym is a good aid in remembering how to keep yourself out of blacklists.

F – Frequency

Check your frequency. If you’re sending emails too often, it’s a red flag to the spam patrol. On the other hand, not sending often enough, you risk that the email addresses will become outdated.

Build a marketing plan that’s relevant to your audience. They probably don’t need to hear from you on a daily basis, but don’t wait two or three months before reaching out again. In this case, out of sight means out of mind.

I – Images

Scale your images. Don’t overload your email with images and graphs, or you risk that they won’t be delivered. On top of rubbing ISPs the wrong way, it overwhelms readers and takes away from the purpose of the email.

S – Subscribe

Ask your email list to add your email to their contacts. This technique is known as whitelisting – it ensures that your email address is identified and received.

T – Test

Make sure you do a round of email testing. Not only is this beneficial from an editorial point of view but it will help you check for viruses that may have been accidentally embedded into the email.

spam statistics


Spam filters

Spam filters are working hard to keep irrelevant information and endless sales pitches out of people’s inboxes. They have a long list of criteria, according to which your email is scored. In this case, you want to keep your score low.

If a reader deletes your email without opening it or marks it as junk, well, then your email not only is doomed for the trash, but it adds unwanted points to your spam score.

In addition to invalid emails, too many role emails i.e. or – also raise the ire of ISPs and are another way to determine a poor quality email list. Keep your list clean, and ISPs will be merciful.

To avoid passing the score threshold, follow these tips:

1) Personalization: Spam filters want to know if you’re familiar with the recipient. Use merge tags to personalize the ‘To’ field of your campaign.

2) Double opt-in: Make sure that the recipients of your email list have opted in to receive these emails, also via a confirmation email.

Double optin mechanism

Double optin mechanism scheme by Adobe

3) Clean content: Spam filters analyze your content. Limit risky words, such as ‘free’ and ‘buy.’ On that note, don’t make misleading claims either. Under no circumstances should the subject line state that a prize has been won, only for the content of the email to state the conditions for redeeming the prize.

4) Recognizable name: This is how you’re representing your company. Do it right. Build a good reputation by using an email address that tells the user who exactly these emails are from or are good examples of professional email names to use.

Do not use obscure names that consist of random numbers and letters and certainly, don’t use a ‘noreply’ email address.

5) Do not purchase emails: Purchasing email lists is a bad idea. Although people like birthday surprises, they don’t like surprises in their email.

People on purchased lists are more likely to mark you as spam. Spam complaints are responsible for up 20% of email deliverability issues. Also, purchased lists are full of spam traps.

Speaking of which…

Spam Traps

Not all deleted email accounts disappear into cyberspace. Some of them are repurposed into spam traps. A spam trap is an inactive email address owned by the ISPs. They use these accounts to catch and punish malicious senders. If you send an email to one of these accounts, ISPs will mark you as spammer.

There are different kinds of spam traps. There are pristine spam traps and recycled spam traps.

Spam traps types

Image source:

A pristine spam trap is created by the ISPs to catch spammers. They appear to be low-hanging fruit, and bot-scrapers pluck them from the tree. However, they are poison fruit to a marketer.

Recycled spam traps are abandoned email accounts the ISPs monitor. Pristine spam traps will damage your reputation more than recycled traps, yet both are ominous for your business.

An abundance of email spam traps in your list shows you’re not using email best practices.

How To Write a Good Email

Link to quality sites – Linking to a shady site is one of the fastest ways to get a content bounce. Also, don’t use link shorteners in your emails. They are great for sites like Twitter, where character count is of importance. However, in email messages, they make you look like a spammer.

Balance the image and text ratio – Emails with too many images can damage your email deliverability. First off, some email clients can’t read HTML or images in emails. If the prospect can’t understand your email, you’re not going to convert.

Also, emails solely comprised of one big image are suspicious to ISPs. Many marketers use image-text to try and dodge the spam filter. However, the ISPs have caught on.

Avoid hashbusting – Certain words can trigger the spam filter. For example – free, fast cash, lowest price, insurance, earn extra cash, etc. Hashbusting is slightly changing the characters of these words to confuse robots. For instance, Free may be written as Fr33. However, ISPs are catching on to these alterations.

Avoid deceptive subject lines – Open rate is one of the most overrated statistics in marketing. If your subject line is “100% Free $50 Visa Gift Card”, you’re going to get a lot of opens. But if you don’t satisfy the reader, you’re going to get marked as spam. A strong offer is useless if you betray expectations and trust.

Avoid Excessive punctuation – Using caps in your email is like shouting. It’s bad practice and it irritates people. It’s also not recommended to use excessive punctuation, such as multiple exclamation marks.

Here’s a great way to test content bounces. If a simple message (like Hi) gets through, but your campaign doesn’t, it’s probably an issue with your content. Use the tips above to stop your emails from bouncing.

Tactics such as these are more likely to have the reader interact with your email. Opening the email, replying to it, moving the email to a primary folder – all these factors that impact your score positively.

Hard bounces and soft bounces

Hard Bounces and Soft Bounces

Hard bounces. Soft bounces. There’s a difference between them but the line isn’t always as clear as you might think.

An email bounce happens when an email can’t be delivered to an email address.

A hard bounce is a permanent error, meaning that email is not good for the indefinite future. A soft bounce is a temporary error. Some of these can be saved and re-added to your campaign. The others need to be removed from your list completely.

Hard Bounces

What does a hard bounce usually mean? It means an email address doesn’t exist. Here are the two most probable explanations.

1) The email was deleted

Maybe a senior executive left his company, and they deleted his email address. Or perhaps an art director deleted her Hotmail address because it was full of spam. Email addresses are deleted and permanently abandoned all the time. That’s why email list decay happens to every marketer.

2) The email never existed

This is usually the result of a typo or human error. However, false emails aren’t always accidental. For instance, a poor prospect might give you a fake email address for your lead magnet (if you’re using single opt-in).

In rare cases, malicious competitors will degrade your email list with false emails and spam traps. Using double opt-in for your email marketing campaigns will curtail this problem.

Clean list is your ticket to a real consumer audience. If emails aren’t real, then there is no audience to interact with. Make sure to keep your list clean and up to date. Fake emails, invalid email accounts or canceled addresses are all mechanisms to generate hard bounces.

Remove them from your list immediately.

Hard Bounce vs. Soft Bounce

Image source:

Soft Bounces

Soft bounces are better than hard bounces because it means a prospect may be salvaged. Unlike hard bounces, you still have a chance to communicate with these prospects.

Many times a soft bounce is a temporary problem on the recipient’s end:

Inbox is full

If your recipient’s inbox is full, they can’t receive messages. A full mailbox is often a sign of an inactive account. However, there are plenty of examples that illustrate the contrary. You can deliver messages to these prospects a few more times, in the hope they’ve cleaned their inbox.

Email server is down

There are many reasons why an ISP goes offline. Sometimes, they are doing maintenance on their server. Other times, their server crashes, is overloaded or is unavailable for an unexplained reason. Once the ISP fixes this short-term issue, you can email your prospect again.

Your message is too big

If your message is too big, it will soft bounce. For instance, Gmail imposes a sending limit of 25 MB, which is actually quite generous. Remember that pictures and videos take up a lot of space. A single minute of 4K video takes up 130 MB, and 1-2 MB is not uncommon for a photo.

If an email soft bounces too many times, you should treat it as a hard bounce and delete it from your active list. Moosend recommends sending four times to soft bounces.

Don’t resend to soft bounces immediately. Hold on for one or two days. Wait until those full mailboxes are cleaned, and those faulty servers are repaired.

Email reputation

The Importance of Email Reputation

Your email reputation is a score given to your organization by your internet service provider (ISP.) A low sender score will lead to serious deliverability issues as ISPs will mark your messages as spam or, possibly, even refuse to send them.

Recognizing a Poor Email Reputation

As an email marketer, it’s your job to understand the different elements ISPs use to calculate your sender score and recognize if and when your organization begins to suffer the effects of a poor email reputation.

A poor reputation most noticeably manifests itself in low open rates. Take some time and analyze your email data.

If your open rate is significantly below the general email marketing average of 25% or steadily declining over your last few mailing, there’s a good chance your sender score has been damaged and is in need of rescuing.

Other signs of an impaired sender score are high bounce rates and significant amounts of spam complaints.

Your overall email reputation is built upon three pillars: the reputation of your IP address and domain, and the level of engagement your email campaigns generate. Let’s take a closer look at each of these:

Reputation of IP address

The “IP” in IP address stands for “Internet Protocol” and internet service providers supply one to every device on their network in order to accurately route user requests.

In regard to your email reputation, the quality of the IP address you are sending from is taken into account by the ISP delivering your emails. If you or other people on the same network, fellow wifi users at a local coffee shop for example, regularly practice poor email etiquette, your IP address reputation will plummet.

Reputation of domain

While it’s not always possible to control the reputation of an IP address, the reputation of a domain is completely reliant upon the person or people using it.

In order to maintain a positive domain reputation, simply follow the good email marketing practices outlined in this email deliverability guide.

Level of engagement

Beyond IP addresses and domains, the engagement level of your email campaigns plays a role in your reputation as well. ISPs want to see proof that the messages you send are enjoyed by the people receiving them.

If you continually mail to dead addresses and receive high bounce rates, or you consistently experience below-average or declining open rates, or there are numerous spam complaints, your ISP will conclude that your messages are not wanted your sender score will go down.

How to Rescue Poor Email Reputation?

As you’ve probably noticed by now, reaching someone’s inbox is much more complex that you would thought. There are several factors that influence whether your email will be delivered and numerous stages of protection fby internet providers from unwanted emails.

In the following diagram, you can see a simplified scheme illustrating the journey of an email to an inbox.

If your email deliverability isn’t where you’d like it to be, don’t worry! There are ways to redeem a poor reputation.

Own the domain: As basic as it may sound, having your own domain is a crucial first step in improving your reputation. If you mail from an @gmail rather than an @yourcompany address, you’ll most likely experience a higher bounce rate and lower sender score.

Receive permission: Every single subscriber on your list should have given you explicit permission to email them. Purchasing or renting an email list from someone else is quite risky and can easily damage your reputation due to the higher probability of spam complaints. Instead, employ ethical list building strategies and ensure everyone you mail to is happy to receive your messages.

Keep it consistent: Your subscribers have short attention spans and if you neglect to email them for a stretch of time, they’ll be much less likely to engage with your content. Develop a regular mailing schedule and stick to it.

Create compelling content: Creating compelling content is a fantastic way to improve the third pillar of a good email reputation: engagement. After all, your subscribers will be more inclined to open your emails and click on links if they enjoy receiving the things you send them.

To do this effectively, you must have a deep understanding of your list and what they’re looking to get out of your emails. You also must do your best to provide personalized experience for each of your subscribers.

Verify your list: Studies show that the average email list consists of 60% of dead leads due to subscribers changing occupations, email providers and more. It means that, for most companies, 6 out 10 subscribers will never even receive the emails they send to them.

While you have no control over when a subscriber changes their email address, you can control whether you keep emailing them or not.

By using an email verification service like Email List Verify, you can quickly and easily purge these dead addresses from your mailing list so that you receive less bounces and your reputation isn’t constantly being damaged.

Offer plain text: Deciding to send plain text over HTML emails is a personal decision every business must make for itself, but, as a healthy compromise, at least offer a plain text version of every HTML message you send. This will ensure that email providers like Gmail and Outlook don’t automatically place your message in the spam folder…


To sum up, for an email marketing campaign to be successful, there are several steps you must go through. Yes, you should still be excited to flaunt your creative talent, just make sure it doesn’t go to waste!

Knock down the ISP blockades, jump through the spam filters with email list verification, and land gracefully in the inbox to get those click-through rates up! Following the tactics and tips outlined in this guide is undoubtedly the way to go.

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