A lot of things can go wrong when you try to send an email to someone, like sending unedited emails or landing in the spam folder.

Proper email infrastructure can help with email deliverability, but asides that, there are some best practices regarding sender behavior you have to stick to otherwise, your email will not deliver, and you are at risk of being blocked by internet service providers.

Table of contents

  • Introduction
  • Infrastructure
  • Sending behavior
  • Content

In this ultimate guide, we will look at all the aspects that influence email deliverability and cover 30 email deliverability best practices to stick to so you can boost your inbox reach.


What is email deliverability?

Improve your Email Deliverability

Email deliverability can be understood as a likelihood that your email will be delivered to the inbox of your recipient. Simply put email deliverability is the probability that your mail will land in the recipients’ inbox not just get delivered.  Many aspects influence whether the email will be delivered or not.

email deliverability scheme

Email deliverability is closely connected to the sender’s reputation. If your sender behaviour follows the general rules and you have proper infrastructure, your sender score will be high, and your deliverability will thrive.

Note: There is a difference between email delivery (number of emails that are received by the gateway server) and email deliverability (number of emails that get to the inbox). This guide is going to focus only on email deliverability.

Why should you care?

Email marketing has a huge potential and offers excellent possibilities to be creative when reaching your customers (or potential customers).

But to reach those people with your top-notch email campaign, your email needs to land in their inbox.

About 270 billion emails are sent every day around the world, half of which are business-related emails, while the remaining half is for consumers.

About 50% of this 270 billion emails are said to be spam which means over 100 billion spam messages are sent every day.

The global inbox placement rate is around 85%, which means that about 15% of the emails worldwide never reach the inbox of their recipients.

Indeed, you don’t want to waste your money and time on email marketing only to end up blocked, blacklisted, or filtered as spam. The issue is that if you practice poor email hygiene and ignore the best practices, it may happen faster than you think. It’s a battle between you and the other 269 billion emails travelling to their recipients.

An undelivered marketing email is a lost opportunity. Undelivered transactional email means a disappointed or angry customer.

It’s all about sender reputation

When it comes to email deliverability, it all revolves around the sender’s reputation. Let’s take a look at what it is, how it influences your deliverability, and most importantly, what to do to keep it at a satisfactory level.

The internet service providers (ISPs – in the context of this guide, we mean email providers such as Gmail, Yahoo, Hotmail, etc.) collect data about your sending behaviour and process them to assign you with a so-called sender score, also known as sender reputation.

There are two main basic types of a sender reputation:

  • IP reputation
  • domain reputation

The main difference between these two is that IP reputation depends on your sending IP address, while domain reputation is bound to your sending domain.

IP reputation

The “Internet Protocol” address is a string of numbers that is a unique identifier for the device you use to send an email. Internet service providers give one to every device on their network to accurately route user requests.

There are two basic types: shared IP address or dedicated IP address.

A shared IP address means that more companies use the same IP address, so your reputation is subject to the behaviour of the users with whom you share the address.

shared IP vs dedicated IP

Domain reputation

Domain reputation is becoming the more popular way of establishing a sender score. It doesn’t depend solely on the IP address, but it considers the domain too.

This means that even if you change the IP address, the reputation is tied to your brand. It is a perfect situation if you have a good reputation. You don’t have to rebuild your reputation from scratch, but it also means that you might get stuck with a bad sender reputation.

Numerous factors influence your reputation. It’s your job as an email marketer to understand the different ways ISPs calculate your sender score and recognize when your brand suffers the effects of a bad email reputation.


Sadly, no matter how great a campaign you have prepared, when you do not have proper infrastructure, your email marketing is bound to fail. In the following tips, we cover the essential email deliverability best practices when it comes to the infrastructure and authentication of your emails.

Update Your Gmail.

Although the technical aspects of email deliverability may seem complicated at first, most of the settings need to be done only once.  Plus some parts may already be covered by your email delivery service.

1. Use a dedicated IP address

Always keep in mind that if you share a sending IP address with others, their behaviour may influence your deliverability too. A shared IP address is not a big deal if you do not send thousands of emails monthly; it would save you some costs. If, however, you rely on email marketing heavily, you should consider investing in a dedicated IP address to make sure there are no other users who could negatively influence your reputation.

2. Use different IP addresses for various email types

You could also consider setting separate IP addresses for your marketing emails and transactional emails.

This is a best practice to make sure that your marketing campaigns won’t influence the deliverability of the essential emails such as password recovery or purchase confirmation.

3. Don’t change your IP address

We know the first thing that probably comes to your mind when you have email deliverability issues is to change the sending IP address and begin all over again with a clean slate. However, it may not be a good idea – this kind of behaviour is very suspicious and may not solve your problem at all. Switching IPs is a common tactic used by spammers, so new IPs are always treated with caution. Spam filters consider the age of the IP as well as the sending permanence.

4. Warmup your IP address

If you need to change your IP address (or you start with a new one), make sure to warm it up first. This means start with sending small amounts of emails then gradually begin to increase the number so that you can establish the initial reputation.

IP address warmup

Source: GlockApps

If you use a shared IP address warmup is not usually necessary.

5. Secure your servers with TLS

Transport Layer Security is a type of encryption that is applied to the email to protect it from being read by an unwanted party during the process of sending (from the moment it leaves the sender until it is received).

TLS- encrypted emails may be preferred by some email servers, so it’s an email deliverability best practice to have this protocol enabled to increase your chances of landing in the inbox.

6. Authenticate your email

Email authentication is a process of improving the delivery and proving the credibility of emails by implementing protocols that verify the identity of the sending domain.

Three fundamental protocols serve to determine who you are – SPF, DKIM, DMARC. They serve as gatekeepers who identify you and decide whether you are a legitimate sender.

Sender Policy Framework (SPF) is a DNS record that informs the provider which IP addresses are allowed to send from your domain.

Domain Keys Identified Mail (DKIM) is an encryption method ensuring that the sent and the received messages are the same, thus preventing the stealing of the identity.

DKIM authentication scheme

Domain-based Message Authentication, Reporting & Conformance (DMARC) record indicates the presence of SPF and DKIM protocols and tells the recipient what to do if these two authentication methods fail. It reduces exposure to harmful and fraudulent messages.

7. Subscribe to feedback loops (FBL)

This rule is pretty simple and obvious- You mustn’t send emails to those who have marked you as spam. If somebody marks your message as spam or trash and you send him another email anyway, your reputation score may suffer considerably

Feedback loop scheme

Almost all internet service providers offer a service called feedback loop (FBL) that will let you know if your email has been marked as spam. Once you are alerted, you should remove the contact from your mailing list immediately. Most mailing services (like SendGrid, MailChimp, or Zoho) do this automatically for you, so you don’t have to manually remove the contacts.

8. Set up postmaster@ and abuse@ addresses

Having these two role accounts is an email deliverability best practice and a requirement by some internet service providers. These role accounts are used to receive abuse complaints so you must regularly check them and resolve all the issues as soon as possible.

9. Use a domain that can receive email

The ISP may automatically block your email if your sending domain cannot receive emails. Therefore, don’t forget to have a valid MX record associated with the domain. Anyone that is getting an email from you should be able to reply to the same email address. Besides, having a “no-reply” address may evoke an arrogant attitude – “We want you to hear from us, but we don’t want to hear from you”.

Sending Behavior

10. Never purchase emails

Purchasing email lists is not a good idea. People on purchased lists are more likely to mark you as spam and damage your reputation. 20% of email deliverability issues are linked to spam complaints and purchased lists are always full of spam traps.

Not to mention the fact that the engagement level is inferior, these people are simply not interested in your product. There are many better ways to spend your money…never purchase emails.

An example of a service selling email lists. Avoid them like the plague.

11. Always have consent

Even if the email address is not purchased but given by its owner, make sure everyone you mail to is happy to receive your messages.

If somebody gives you an email to register for your service, it doesn’t mean he/she is interested in your monthly newsletter. The same applies to giveaways or lead magnets.

You should have received explicit permission from every single subscriber on your list to send them a specific type of email.

Instead, employ ethical email list building strategies. It is better to have a handful of happy recipients than thousands of people who are not interested in your marketing emails.


In 2018, a new General Data Protection Regulation (GDPR) came into force in the European Union. It applies to all businesses in the EU (or companies doing business with the people in the EU) and defines how personal data can be handled and used.

One of the essential requirements of GDPR when it comes to email marketing is to have explicit consent from every contact that ends up in your database.

GDPR compliant form

An example of a GDPR compliant email form. Source: SuperOffice

12. Don’t be afraid of unsubscribes

As we mentioned previously, when it comes to mailing lists quality is more important than quantity. If someone doesn’t want to receive your emails anymore, make it as easy as possible for them to unsubscribe – otherwise, they will use other options (junk, spam folder).

email unsubscribe

A typical unsubscribe link at the bottom of the email

The best email deliverability practice is to have an unsubscribe button at the bottom of every marketing email you send. Do not require a login, do not force the contact to fill a lengthy form explaining why they don’t want to hear from you anymore (or at least, make sure the form is optional).

If someone doesn’t want your emails, you shouldn’t want to have them on your list. An easy option to unsubscribe is suitable both for you and the user.

13. Use double opt-in

It is considered a best practice in email marketing to prevent sending to people who did not give explicit permission – e.g. if person A signs up person B for a marketing newsletter on a particular website. To be sure you are sending only to those who are interested in your emails, go even further and implement a double opt-in.

Double opt-in simply means a second confirmation of the email preference that is sent to the recipient’s inbox and has to be confirmed sending. Only after this action, will the contact will be added to the mailing list.

Opt-in scheme

14. Be consistent

It is essential to consistently stick to your sending schedule regarding both the volume and frequency.

Create a plan and stick to it. The best email deliverability practice is to send one or two emails per week. If you select a particular time, people will know when to expect your emails.

It is suspicious when you are inactive for a month or more and then start to send 3-4 emails a week; it may lead to a lower sender score given by the ISPs. The same applies to rapid spikes in the volume of contacts in your sending list.

15. Be careful about spam complaints

One of the most vital signals for ISP’s to lower your sender reputation is when you’re actively being marked as spam by the receiver of the email. The absence of an unsubscribe link, is one of the many reasons why you may often be marked as spam.

SPAM button Gmail

A Spam button in Gmail

Make sure you check the spam complaint statistics regularly and keep the spam complaints low. Of course, it is tough to keep the rate at 0% but in general, try to keep the spam rate below 0.1% (for example, a spam complaint rate higher than 0.08% already affects your deliverability in Gmail).

16. Avoid being blacklisted

There are hundreds of publicly available blacklists that gather the email addresses that are “confirmed” spammers. Most often, they are based on spam complaints and spam traps hits.

Some of the blacklists only last for a day or two. Other custom blacklists have longer bans, and ISPs check them as one of the ways to find unwanted senders. There are blacklist checker tools you can use to see whether your email address is on any blacklist.

Most common blacklists

Source: ReturnPath

If you’re on a blacklist, try to figure out the reasons why it happened and fix the issue. Then contact the list owner with the request to delist you.

Of course, prevention is the best strategy. This is why you should follow the best practices stated in this email deliverability guide.

17. Avoid spam traps

A spam trap is an inactive email address owned by the ISPs. Spam traps are used to catch and punish malicious senders as they are sure the email address could not have been obtained in a traditional, legitimate way.

The one-way ticket to a blacklist is sending an email to a spam trap. You are very unlikely to get one into your email list if you stick to the ethical ways of getting email contacts. Again, never purchase or harvest emails this point cannot be overemphasized.

18. Keep the bounce rates low

An email bounce happens when an email can’t be delivered to an email address. Two types of email bounces could occur.

A hard bounce is a permanent error, meaning that email is not good for the indefinite future. You should remove the hard bounce email from your list immediately.

A soft bounce is a temporary error. Some of these can be saved and re-added to your campaign. However, don’t resend to soft bounces immediately. Wait for one or two days until those full mailboxes are cleaned and those faulty servers are repaired. Although soft bounces today occur when there is a sudden increase in email sending volume like we said in a previous point ISP’s like consistency.

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

Hard bounces vs soft bounces

19. Keep an eye on the engagement

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.

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

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

Average results in email marketing

Source: GetResponse

If your open rate is significantly below the general average of (usually around 20% – 25%) or steadily declining over your last few campaigns, there’s a good chance your sender score has been damaged, and you need to change your email sending practices.

20. Get rid of inactive subscribers and role accounts

If someone doesn’t open a single email from you for several months or even more than a year, its either they are no longer interested in your emails or the email address is no longer used.

Set a reasonable period and clean your lists from inactive contacts to make sure your engagement levels remain high. The same applies to role accounts such as [email protected] or fake emails such as [email protected].

21. Verify your list

An email verification tool is sure to help you to find and get rid of all spam traps, hard bounces, typos, and disposable or catch-all emails.

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 of 10 subscribers will never even receive the emails they send to them.

You may not have control over when a subscriber changes their email address, but you can control whether you keep sending them emails or not.

By using an email verification service like Email List Validation, it’s faster and easier to purge dead addresses from your mailing list so that you receive fewer bounces and your reputation isn’t continually being damaged.

22. Be careful with the re-engagement campaigns

The re-engagement campaign is an email campaign in which you try to win back the contacts that were once active but have become uninterested over time.

These campaigns are risky – they can have a high spam complaint ratio and very low engagement. It is a good email deliverability practice to use a separate IP address for these types of campaigns so that their failure won’t hurt your primary sender score.


The content of your emails is another factor that could influence your reputation score.

Creating compelling content is a fantastic way to improve engagement, but it is not the only thing you need to focus on. Emails with poor content, bad formatting, and other signs of spammy behaviour can damage your deliverability too.

Check the following tips to stop your emails from being filtered by ISPs.

email verification online

23. Format your email properly

There is an old debate about plain-text emails vs HTML emails. Both have some advantages and disadvantages, but people tend to prefer friendly, formatted emails with images. Using HTML emails won’t hurt your reputation, but when you want to use HTML emails, you must make sure the code is clean. Broken HTML tags are detected easily by ISPs and will hurt your deliverability.

As a compromise, you should 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

Subscription settings

An example of email preference settings with the option to select email format

24. Balance the image and text ratio

Do not jam-pack your emails with images; this 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, avoid putting one big image in your emails; it is suspicious to ISPs. Many marketers use image-text to try and dodge the spam filter. However, the ISPs have caught on.

25. Segment and personalize the emails

We already mentioned that it is good to segment the emails into marketing and transactional/administrative emails and use different IP addresses for them.

However, email segmentation can be taken even further. You can segment your contacts based on many other aspects (gender, age, engagement). Divide your list into smaller segments and add a touch of personalization to your emails. You can decide to mention every receiver’s name make them feel special.

This will increase the open rates of your emails, and you won’t send the same message to all your contacts, which is something that may alert ISPs if done on a large scale.

26. Limit risky words

Spam filters analyze your content. Limit risky words, such as “free”, “lowest price” or “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.

Here is a list of risky keywords you should avoid using in your emails collected by Mailjet:

Spam words table

27. Link to quality sites

One of the fastest ways to be filtered as spam is linking to a shady site. If you want to link to an external source, make sure to link to a website that has a good reputation.

Too many links in your email may look suspicious, consider the number of links in your message before you hit send.

28. Don’t use link shorteners

Link shorteners are great for sites like Twitter, where character count is of importance. However, in email messages, they may lower your sender score as they are often used by spammers to hide shady links. Do not use them.

29. Avoid deceptive subject lines

The open rate is an important metric, but you should not try to improve it artificially. 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. It’s the best email deliverability practice to earn your receivers’ trust. A strong offer is useless if you betray expectations and trust.

Deceptive subject line

An example of a deceptive subject line trying to evoke the impression of an ongoing conversation

30. Avoid excessive punctuation

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