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Ultimate Email Deliverability Guide

On January 21, 2021
14min read
Piotr Malek Technical Content Writer @ Mailtrap

In the fight against spam, ISPs (Internet Service Providers) put more and more restrictions on access to the user’s mailbox. This all works to the users’ benefit – it lets them have a clean mailbox with content they want to receive and an experience they expect from a mailbox. But time and time again, important messages miss user’s inboxes due to sometimes foolish mistakes the senders make when in a hurry or due to lack of experience. Don’t let this happen to you. Bear with us as we cover the basics of email deliverability, suggest what to focus on and what to avoid.

Why email deliverability matters?

A user forgot her password? Send her an email with reset instructions. A new feature was just launched? Deliver the good news to the inboxes of your community. The traffic on the blog is slower than usual? Send a roundup of the latest articles to your mailing list. Companies send emails all the time.

Yet, according to the latest annual research from Return Path, only 85% of legit emails reach their final destination. This means that, on average, every 3 out of 20 users (or a whooping 15,000+ users in a seven-digit community):

  • won’t regain access to their account immediately and might abandon your platform
  • won’t know about that shiny new feature you’ve worked on for months and might flip to competitors offering the very same or even a less functional option 
  • won’t be reminded of your existence and won’t even consider one of your paid plans

If you can afford not to worry about it, we envy you. Most content specialists, however, will do their best to boost their delivery even by a single percent. At Mailtrap, we deal with emails on a daily basis and we wanted to share the key things to consider when trying to improve deliverability.

As there are plenty of things to consider, we’ve split them into sections and for each, we’ve assessed how easy it is to implement them (skill-wise) as well as how time-consuming and how important they are for your success. For each, we use a scale of 1 to 5, where ‘1’ means a very difficult and time-consuming implementation as well as the least important. ‘5’ means a really easy and quick fix and also high importance. Let’s start!

Part 1 – Building the right reputation for your email campaigns

Easiness to implement: 1 / 5 (doesn’t require any tech-savviness)

Time to implement: 5 / 5 (building a reputation takes time)

Importance: 5 / 5 (reputation is everything)

ISPs care a lot about the credibility of your domain and IP address. Before any email is delivered, they’ll run a so-called ‘reputation check’ to evaluate if you’re likely to be sending unwanted messages or might have some nefarious motives for contacting your mailing lists. If they deem you do, your deliverability will likely suffer.

To avoid such a fate, focus on building the right reputation from your first campaign:

Send emails only to users who want to receive them

While buying mailing lists is an obvious no-no, you should also be careful about emailing people who didn’t give you explicit permission to do so. Just because someone joined one of your events a few years back or signed up on your forums back in 2010, doesn’t mean they will appreciate being notified about your new product launch. If they don’t, they’re likely to mark your message as spam to get it out of their inbox. Even a few such requests are enough to significantly harm the reputation of your domain and get you blocked on future campaigns. Try to resist the temptation of contacting random accounts who MIGHT be interested in what you have to say (but likely are not).

Make it really easy to unsubscribe

This might sound counterintuitive. After all, you’ve been working so hard to gather your mailing list, why would you let them go so easily now? 

You’re probably also subscribed to some mailing lists (voluntarily or not) but hardly ever even open their emails. It could be that you signed up to access some e-book or tried a product years ago but don’t really care about it anymore. Or maybe you were genuinely interested in some blog but, for whatever reason, just can’t be bothered anymore. 

There are hundreds of such people on your list and if they don’t interact with you now, there’s a close-to-zero chance they will in the future. If you make it hard for them to remove themselves from the list, sooner or later they’ll hit the ‘spam’ button and quit anyway. What’s more, ISPs also look at whether people interact with your emails when assessing your reputation. If they never open them, it won’t help your cause. 

(one-click unsubscribe from Trello newsletter, really good experience and easy to fix if you unsubscribed by accident)

One thing to keep in mind – people might not necessarily want to unsubscribe from all your communication. Chances are they’re just receiving too many emails or are more interested in a different area that you also cover with your content. Consider setting up a simple ‘preference center’ where users can decide what they wish to receive and how often. Everyone likes being in control and some will stay with you for longer if you give them that option.

(HubSpot gives you a choice. There were 44 positions on the list. Wow)

Purge your lists

Letting people unsubscribe easily is not enough. You should also remove some contacts on your own. Talk about going against the grain!

Believe us or not, it makes a lot of sense. The obvious case are bounces. If your mailing software doesn’t automatically remove accounts that bounce, do it manually. Even several bounces from one campaign can cost you a serious chunk of the reputation you’ve worked so hard to gain.

Nearly any software for sending mass emails such as MailChimp or SendGrid offers detailed stats for each of your campaigns and accounts involved in each. You can easily check who opened your emails, who clicked on the links and how many times they did either. This lets you quickly determine who hasn’t been active for ages and is just decreasing the quality of your list. Remove such users every now and then and focus only on those that appreciate your content. 

Protip – some companies go as far as sending the inactive users an email saying, literally, “Hey. We’ve noticed you didn’t open any of our recent emails. Should we not bother you anymore?”. What are the two most likely outcomes of such a message?

  • the user unsubscribes and, as a result, improves the quality of your list
  • the user stays on the list and actually starts interacting with your content

You win in both situations.

It could also be that these people don’t open your emails because… they’re not receiving them in the first place. Read on as we’ll be sharing many more tips on getting your emails delivered.

Follow a consistent schedule

Both users and ISPs appreciate companies that follow a regular schedule of sending emails. Users are also more likely to open and interact with emails when they come at a regular schedule, for example, every Tuesday afternoon. If you send usually one email a week but suddenly switch to three, it might sound suspicious to the email provider. Resist the temptation of letting everyone know right away about a brand new product. Instead, integrate such a message into your existing campaigns.
Another reason to send emails at the right time is to increase conversion and improve your reputation. That 10-11 am period on Tuesday sounds like a good start. Many tools for sending emails let you send them at a specific time in the user’s timezone. If you have a distributed list from very different time zones, this will be a must.

Avoid spam traps and blacklists

Spam traps are fake email accounts set up by ISPs and placed in various locations around the web. While harvesting emails, bots also tend to add these addresses to their collections as they look no different than the real accounts bots are after. Send a single email to such an account and your deliverability will immediately suffer.

Those making such foolish mistakes and many other spammers end up added to multiple blacklists. Many email providers, before delivering an incoming email, check against those blacklists and decline emails if they find enough reason to consider someone a spammer. Needless to say, you don’t want to be on any of these lists.
MX Toolbox has a free tool for checking if your domain already ended up on one of the blacklists.

(ugh, we’re safe ;-))

Part 2 – Infrastructure Factors

Easiness to implement: 4 / 5 (requires involvement from a dev team)

Time to implement: 3 / 5 (for someone tech-savvy, it’s fairly easy). 5 / 5 if you opt for a private IP.

Importance: 4 / 5 (the right infrastructure matters a lot)

Now, let’s look at a bit more technical aspect of getting your emails delivered to inboxes. Spambots, in an attempt to get users to open their emails, are known to try to impersonate real people or organizations. A phishing email sent from with a request for donations is much more likely to bring $$$ than the very same email sent from

To prevent that, ISPs implement several types of authentication techniques to ensure the email originator is real. It’s quite easy to pass them if you’re a legit sender so definitely invest a bit of time into this.

Authenticate with DKIM

DKIM stands for DomainKeys Identified Mail and is used to validate if a given email message was indeed sent by the owner of a given email address.

It’s a digital signature that’s sent with every email message sent. It includes encrypted details such as message body or/and headers, sender’s domain and others. When an email with DKIM is received by an incoming server, it will recreate the signature with a public key and compare it against the DKIM received. If there’s a match, an email will get a significant boost to deliverability. If it fails, it will be a hint for a receiving server that the sender might not be who he/she claims to be.

If DKIM is missing, it might not disqualify a message but will affect its deliverability.

Authenticate with SPF

SPF (Sender Policy Framework) is another important authentication method. Unlike DKIM, it doesn’t include any information about the domain or address that an email is sent from. SPF records, however, tell an incoming server which hosts (or IP addresses) are allowed to send emails with a given email address. Before an email appears in a mailbox, an incoming server does a quick check. If things just don’t match, an email might be rejected right away.

Which one should I use – DKIM or SPF?

Both. While they might seem like competing services, they’re in fact best used simultaneously. DKIM is unable to verify who sent a message and SPF does it really well. On the other hand, SPF doesn’t include any body and headers’ verification but that’s what DKIM was made for. Using both makes it fairly clear to incoming servers that your emails are legit and you are who you claim you are.

Authenticate with DMARC

Just when you thought you were done with authentications, DMARC appeared on the horizon. And rightly so. DMARC is the most sophisticated of all three methods because it leverages both DKIM and SPF and adds an extra check (known as ‘alignment test’) on top of that.

DMARC also allows you to tip a receiving server on what it should do if an email fails the test. Such messages can be either discarded right away, sent to a quarantine (usually a spam folder), or treated as usual. Finally, for each test failed, a sender might receive a report with the details of what happened, providing a first-hand source of knowledge if any spoofing occurs or a legit email fails a test.

DMARC requires at least one of the previous two methods to be implemented. It certainly won’t hurt to have all three set up for better credibility and protection from cybercriminals.

Rely on double opt-in

Another thing worth setting up for any email campaign you’re planning to send is a double opt-in. Typically it means that after a user signs up to receive your emails, they need to head over to their inbox and confirm the intent.
While adding a plain functionality doesn’t affect your deliverability, it affects the quality of your mailing list, the number of bounces, and spam reports. While it might be tempting to automatically subscribe people to a newsletter when they register for an event or open an account, you’ll get better results long-term if you explicitly ask them for consent. Doing so also keeps you compliant with the law.

Check feedback loops (and make use of them)

Nearly all major ISPs give you access to feedback loops. These are not some secret channels that users use to give you valuable feedback about your product. These are these simple surveys that users are asked to fill when they unsubscribe from a mailing list and can provide lots of valuable data. Do users complain about getting too many emails? Try decreasing your volume a little bit. Do they claim they never signed up to your list in the first place? Double-check if you’re sending your campaign to the right audience.

Decide between Shared and Dedicated IP addresses for sending

Remember, your IP address also impacts the sender reputation that comes with each of your emails. Platforms for sending mass emails offer by default shared IPs that are used by hundreds or thousands of their clients. This keeps the cost of the service low but doesn’t give you any control over the reputation of a given IP.

The operators, however, do their fair share of quality control and rotate with hundreds of IP addresses to always ensure good deliverability for their clients. For nearly everyone, shared IP will be perfectly sufficient.

However, if you already have hundreds of thousands of contacts on your lists and need to reach out to them on a regular basis, consider investing in a dedicated IP. This will give you full control over your reputation. It’s important, though, not to email the entire list on day 1. Receiving servers need to be taught first who you are and that what you send is legit and desired by your audience. Companies typically start with sending small batches of emails to some of their contacts and, step by step, increase the volume.

Part 3 – Content factors

Easiness to implement: 2 / 5 (requires a bit of research but still fairly easy)

Time to implement: 3 / 5 (needs a bit of a setup and, as mentioned, research)

Importance: 3 / 5 (not as relevant as the first two parts but still need to be considered. Especially since they don’t require a lot of effort)

Now, let’s discuss how to improve deliverability when creating the actual campaigns.

Use branding and personalize ‘from’ field

We mentioned earlier that one of the factors impacting the sender’s reputation is whether users interact with the content or not. One of the time-tested methods to increase the open rate is to include both your company name and the name of the sender. “John from Mailtrap” will likely have much more success with our mailing list than “John Smith” or, worse, “johnsmith48782”. The company name adds credibility and a familiar feel while a person’s name makes it sound as though it’s not just the marketing team sending a new campaign but a regular person behind it.

Of course, you don’t always need the CEO to personally compose and send each email, especially if you send onboarding messages to thousands of users, it’s virtually impossible. It’s fairly common to receive an email from a CEO, respond to it, and be connected with the support team. And people are fine with that!

Inspect Your Emails

Send a welcome message

Right after someone signs up to your mailing lists or registers for a trial account, let them know what they should expect from you. Send them a personal ‘thank you’ for trusting you with their time and let them know what’s coming up:

  • When will you be contacting them (“we’ll be reaching out every Tuesday and Thursday afternoon to…”)
  • What are you going to write to them and why (“we’ll send you various tips on how to get started”, “we’ll send you a weekly roundup of our best content to keep you up-to-date”)
  • Giving them a choice (“if this sounds like too many emails, update your preferences here”)
  • And something to start with (whet their appetite ;-))

Emails like this are an easy way to quickly start a relationship with a reader, to gain their trust, and let them know that they’re in charge.

Avoid spammy titles

If you’ve got a legit mailing list and interesting content, you shouldn’t have to use  BuzzFeed-like expressions to get people to open an email from you. Spam filters are known to take topics and content into consideration. So even if you have a great reputation, full set of authentications and a highly engaged list, sending one “you won’t believe your eyes” email might fail to get it delivered.

Send relevant content

People signed up to your list for a reason and hearing about the great deals for your product wasn’t probably one of them. Don’t misuse their trust. If you promised to send tips and tricks on using your product, don’t turn it into a sales channel. If your users signed up to get your latest blog posts, they will expect to get those blog posts in every email you send. If you fail to deliver on a promise, they’ll either leave (bad news) or mark you as a spammer (worse news).

Of course, you might mention a deal or related product every now and then, but keep it to the minimum. The 80/20 rule applies well here as well. Keep 80% of the content for the relevant stuff and the other 20% for the content more related to your business goals. This can mean that one out of five emails is a bit ‘off topic’ but probably a better choice will be a small section in most emails with a gentle CTA to buy your product/service. Either way, test your feedback loops to see if such messages resonate with the audience.

Segment the list

Don’t just send emails to all your contacts, hoping there will be some interest. Segment users based on their interests, types of features they use, and content they interacted with in the past. The better you understand your audience and the more relevant content you send, the better reception you’ll have at the end of the day. Use analytical tools like Mixpanel to see exactly how users navigate around your platform and apps. It will give you tons of data on what they’re interested in and will let you adjust your content accordingly. If you run several blogs or have multiple content strategies, try to also target content to specific groups, rather than to all your contacts at once. A bit of effort can yield some pretty nice results.

Don’t use no-reply emails

Unless you’re a giant corporation sending out its press releases to millions, you likely want to hear back from users. Whether they come with questions about a product, complaints about too many emails, or feedback/feature requests, the information can be very valuable. While not of a significant value, ISPs also tend to favor those who send emails and accept responses with legitimate addresses.

Which tools to use for email sending?

There are many, many options available. Many offer free tiers for those sending few messages. Each comes with a free trial so you can test the capabilities of a given software. It’s important to choose credible tools with an established reputation of IP addresses and features that match your business needs. These platforms employ many email deliverability experts so they can also assist you in improving your campaigns. Here are a few of our recommendations:

  • SendGrid is one of the biggest players on the market that specializes both in transactional emails and marketing campaigns. You can use their robust API to connect their features to your platform. SendGrid also offers various tools for designing beautiful and successful emails.
  • Sendinblue also offers both transactional and marketing communication. It also comes with plenty of additional capabilities, such as SMS messaging and marketing automations.
  • Mailchimp has all the tools you could think of for building marketing campaigns and automations. This includes templates, a drag & drop email builder and detailed analytics. Mailchimp also owns Mandrill, which is one of the most popular tools for sending transactional emails.
  • Mailjet is another of the popular tools for sending both transactional emails and regular newsletters. It’s probably the most affordable of all these tools while offering similar capabilities.

How to test email deliverability?

Now that you’ve implemented all those tips and tricks, it’s time to build a proper email deliverability test and measure how your emails perform. Luckily, there’s a number of tools, many of them free, to check at least some aspects of deliverability.

Sender Score lets you assess your domain reputation and gives its “Sender Score” for each IP address that you’re known to be sending emails from. On a scale of 1 to 100, the higher the score, the more likely an email is to be delivered. Aim for something in the range of 90+ if possible. On top of that, Sender Score verifies if you’re properly authenticated and if your website has the right certificates.

MXToolbox is a set of tools for validating the reputation as well. We’ve mentioned earlier their Blacklist tool but they also have others for validating your authentications or checking the domain health (among others). and are some more tools for basic reputation checks. You send an email to an individual address and within seconds get a detailed report with hits on what to improve. Make sure you send an actual email with the content you’d like to deliver to readers as the tools analyze the content too. Spamcheck by Postmark works in a similar fashion.

Use Mailtrap to set up a fake environment for testing your email workflows. Check how emails look in various clients, analyze their spam score, and test if they’re properly delivered, without risk of spamming real users.

Try Mailtrap for Free

How to track email delivery?

Finally, if you tested all your campaigns before sending and the results are satisfactory, you probably want to know if the emails were indeed delivered.

There’s no way to know if an email landed in an inbox, not in a spam folder for example. But it’s become an industry standard to track if an email was opened or if links were clicked. Nearly every major email software comes with such analytics built-in and there’s a number of tools such as SalesHandy, Mailtrack to add them to your personal mailbox.

To enable tracking, sending platforms usually attach a tiny, transparent tracking pixel to emails. This file, usually the size of 1px to 1px, is invisible to users, doesn’t affect the deliverability, and is able to let the platform know immediately when an email is opened and links are clicked. It also lets you understand the users better, know which device they use to open an email, what the operating system is, and which app they use for this purpose. Unlike cookies on websites, there are no laws regulating tracking pixels (yet) so you’re free to use them with all your campaigns, without the need to ask for users’ permission.


This sums up our guide to email delivery. We hope the tips presented were useful and helped you improve your delivery rates. Be sure to also check out our other articles, each of which is focused on different aspects of sending emails. If there’s any topic you would like us to cover, give us a hint at

Article by Piotr Malek Technical Content Writer @ Mailtrap