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Everything you need to know about email deliverability and open rate

by Karan Sharma
last updated on Oct 10, 2023 2:53:59 PM

Heads up: this is a long (~9000 words) blog post so I’ve added topic headings in the list to the left with the key points from each topic. The list will also contain anchors links that will allow you to jump back and forth to read the content as you wish or to read only what is interesting for you (I think all of it is interesting, but then again I’m a bit of an email-geek).

Before we start, let me say a few words on why email deliverability and high open rates are key to all email outreach and how it impacts campaign performance.

Consider the following:

Any email that is not delivered into the inbox of the intended recipient will not be opened. Stronger still, even the subject line snippet of it will not be seen by the intended recipient. Effectively, those prospects are not part of the overall potential of the campaign.

What is email deliverability?

Email deliverability is when a sent email gets delivered into the recipient’s inbox. It’s important to note the difference between an email being delivered to their inbox and being delivered to their mailbox.

Inbox placement is crucial and is what will influence your open rate. You may notice a high email delivery (different to email deliverability) but this may mean your email is being delivered to the recipient’s spam, promotions or junk folder.

You need high email deliverability as it will lead to more open rates, thus, more successful email marketing. Let’s take a look at the case for high email deliverability.

The case for open rate

Let’s say that you targeted 1000 prospects and your open rate (due to a variety of reasons) was 30% (very close to the industry average). What that means is that from the 1000 only 300 will actually get to read your content and the other 700 will remain oblivious to who you are and what yo do. Furthermore, since only 300 will actually view your content only they have any chance to reply to you so whatever amount of replies you get will be from those 300 prospects that viewed your message.

Now let’s say you had 15 positive replies so 1.5% (15/1000) of the campaigns total prospects pool – we call that prospect to positive reply rate. The same 15 positive replies can also be expressed in open to positive reply which in this case is 5% (15/300).

Now imagine that you made bunch of improvements and pushed that open rate by 30% to 55% (right at the center of our open rate spread of 40-70%). Assuming you didn’t use click-bait tactics to increase that open-rate, and all other things being equal, you will get the same open to positive reply rate (5%), meaning you will get .05 * 550 = 27.5 positive replies. Even though your open to positive reply rate stayed the same, your prospect to positive reply rate went from 1.5% to 2.7%.

Open rate is the first measure of success (assuming you’re not using it as a vanity metric or using click-baiting tactics) that you need to keep in check. Don’t settle for 30%, when we know that 40-70% is quite common when done things the right way.

Okay, so now that you are with me on the importance of deliverability and open rates. Let’s dive really deep into the factors that impact open rate.

The case for high email deliverability

You may want 100% email deliverability, but this is simply not realistic for reasons you cannot control such as the recipient’s mailbox being full or strict email security blocking external email coming in. However, there are many factors you can control which will be discussed in this post to help you achieve high email deliverability.

Targeting the same 1000 prospects with 30% open rate, 300 people would have read your email. However, this is only assuming that you had perfect email deliverability. Suppose you had a deliverability rate of 80% where the other 20% was sent to spam, blocked or you had an invalid email address, the actual number of email opens would be 800 * 0.3 = 240.

Using the same open-to-positive reply rate of 5%, the number would drop to 12 positive replies from 15. The difference may seem small in this example, but over months or years and multiplied by the number of sales reps, the amount of lost potential revenue can be very significant by simply not following some avoidable factors.

Okay, so now that you are with me on the importance of deliverability and open rates. Let’s dive really deep into the factors that impact open rate.

What are the factors that impact open rate

Firstly, deliverability and open rate are not the same thing. They are closely related where deliverability strongly influences open rate (not the other way around). Further in this article, I list a set of those factors however there are some that won’t make that list because they are simply random or cyclical. One such factor is out of office or auto-replies which may be higher in holiday periods than in peak times.

Technical set up – the back-end framework you need to have to ensure your emails are trusted and secure

Now, we’ll talk about your technical set up. To protect recipients from receiving emails for spam, fraud and spoofing, email authentication has become hugely important not just for security, but also for the success of your email deliverability.

The recipient’s mail server checks all incoming emails and takes into account many different factors to determine the sending reputation. 

SPF (Sender Policy Framework)

SPF is an email authentication method that defines which servers can send emails using your domain (e.g. Without SPF, spammers or hackers may send emails from their own server using another company’s domain as their email address.

To prevent other people from using your domain to send emails, you use SPF. It is a record on the DNS that specifies which servers are authorised to send emails using that domain. It also allows the recipient’s email server to confirm the email they received is from an authorised source.

DKIM (Domain Keys Identified Mail)

DKIM is an email authentication technique that allows the receiver to validate whether that email was really sent by the domain owner. When emails are sent, they can be intercepted by criminals or other illicit third parties during the process of it being transmitted from the sender to the receiver.

To secure the email, two keys are created as part of this authentication method. One private key is created on the sender’s server and another public key is created and saved on the Domain Name System (DNS – like a phonebook on the internet of domain names e.g.

The sender will sign their email with their private key. When the email is sent, the recipient’s email server will receive a DKIM-signed message where it can validate that email using the public key that is available on the DNS. These keys are then combined together to verify that the email is safe and will be delivered to the recipient’s inbox.

Data quality – a key aspect of email deliverability and open rates by ensuring the right people are targeted

Data is a crucial part of the outbound sales strategy and the data you use will directly influence your email deliverability and open rate. You can read more about B2B data in this post, but the following will be a summary of some of the key things to have in your B2B data.

Data relevance

Targeting the right people at the right companies requires you to correctly identify who your ideal customer profiles are. Sending emails with your proposal to people who have no need or use for your product or service is a sure way to get your emails marked as spam. You must ensure you are using relevant data for your solution as this will not only keep your open rates up but also give you a way to tailor your message to your target persona.

Data accuracy

With a list of relevant data, the next step is to make sure your data is correct and up to date. Validating your email address is always good practice before starting any email marketing campaign. Sending emails to an invalid email address will impact your domain reputation and hurt your email deliverability.

Sender reputation – a score that determines the reputation of your email address

Sender reputation is the reputation of your email address and is a score calculated on a scale from 0 to 100 that an internet service provider (ISP) assigns to you. It plays a critical part in your email deliverability as the higher your sender reputation the more likely your email will be delivered to your recipient’s inbox. Conversely, a lower sender reputation will result in lower email deliverability where your email could be sent to a spam folder or even rejected.

Here are a few factors that can affect your sender reputation.

Email engagement

A couple of important factors around email engagement are email opens and replies. Both these metrics show the ISP there is engagement with your emails and thus strengthens your reputation. Using poor quality B2B data or sending irrelevant email content will quickly damage your reputation as no-one will open your email, let alone reply back to you.

This post talks about the key metrics that matter in your campaign and what results are recommended for you to get – here is a quick rundown:

  • Open rate

Between 40 to 70% of emails sent; anything below is abnormal and should be fixed, anything above is welcomed but is usually an outlier.

  • Bounce rate

Under 5% of emails sent; anything above is a bad sign and should be fixed as soon as possible.

  • Reply rate

Between 15 to 30% of emails sent; anything below is a problem and should be fixed, anything above is welcomed but usually an outlier; positive replies should range from 0 to 7%.

  • Reply-to-demo ratio

For every five non-negative replies you schedule one demo; anything worse should be looked at (some industries have lower conversions), anything better is welcomed but usually an outlier.

  • Demo-to-close ratio

For every four to six demos, you close one deal; anything worse should be looked at (some industries have lower conversions), anything better is welcomed but usually an outlier. 

Spam complaints

Sending emails to people you don’t know is a large part of what an email marketing campaign is about. However, it’s vitally important your emails don’t get marked as spam as that will destroy your email deliverability.

There are 2 types of spam complaints: external and internal.

An external spam complaint is when someone manually marks your email as spam. Just because someone doesn’t know you won’t necessarily mean they will mark your email as spam.

An internal spam complaint is when someone unsubscribes from your email and then selects the reason as spam. The option to mark it as spam alerts the sender without the email provider knowing which avoids hurting your reputation.

Spam traps 

Another way ISPs catch spammy email marketers is to set up spam traps. These are email addresses that are owned by an ISP which are either newly created or abandoned old email addresses taken over by an ISP to trap spammers.

Sending an email to a spam trap alerts the ISP that you are likely sending spam and can lead to being blacklisted. When obtaining poor quality email addresses, spam trap emails can also be obtained unknowingly.


A blacklist is a list of IP addresses, sender domains and servers that are identified to send spam. Ending up on a blacklist can have significant impacts on your email deliverability as you may find your emails hitting the junk folder or not being delivered at all.

Blacklists are mainly used by internet service providers or email providers to stop spammers from sending mail and protect the recipient from being a victim of spam or fraud.

Although you are not sending spam emails, if your emails appear to have similar characteristics to spam then there is a possibility of being blacklisted. As well as the previous points, here are a few other characteristics:

  • Growth spike in sending

Extremely large spikes in sending emails within a short time will indicate to ISPs you are likely to be sending spam emails.

  • No unsubscribe button

Having an unsubscribe button is really helpful to recipients who don’t want to receive emails from you anymore. Without it, they would have to mark your email as spam which would seriously damage your sender reputation.

  • High bounce rate

A high bounce rate indicates to ISPs that poor quality data is being used for marketing purposes. It may look like the sender is using a bought list which is common with spam.

Bounce rate – a lesser known but a greater cause of low open rates

Right off the start, let’s note that there are two types of bounces, ‘soft’ bounces and ‘hard’ bounces. A hard bounce represents an email being sent to a wrong and non-existent email address resulting in a delivery failure, whereas a soft bounce can happen for many reasons other than the wrong email address.

Let’s talk about them in the order of less severe to really severe.

Soft bounces

Soft bounces can occur for various reasons which can impact your email deliverability even if the email is correct, a few examples of soft-bounces are; message being rejected because your domain rating is too low, or because the inbox of the recipient is full, or your DMARC record has a very rigid policy, or the recipient’s server setup auto rejects or forwards messages automatically based on some conditions. The list continues. The impact of soft bounces is not really as detrimental as a hard-bounce.

All bounces, regardless of whether they are soft or hard, will lower the overall success of your campaign by shrinking the overall potential over your dataset and decrease email deliverability. Consider the following example: you emailed 100 people but 5 bounced so only 95 of them actually received your email and therefore have a chance to read your email, so in essence, the overall potential was shrunk by 5%.

Hard bounces

A hard bounce represents an email being sent to a wrong and non-existent email address resulting in a delivery failure.

Hard bounces go a step further in causing damage to your email deliverability and overall email marketing efforts which is why it’s important to keep the bounce rate below 5%, which we have found to be well below the line that is dangerous.

Hard bounces impact the domain health and the spam rating of your subsequent emails. Basically, the recipient’s server will be considered a hard bounce as a negative factor and the higher the bounce rate the more point will be removed from the domain rating of the sender’s email address.

Let’s consider the following example, you mailed 100 prospects from which you had the wrong email address for 15 of them, so in this example, you had 15 hard bounces. The consequences of those 15 hard bounces are that, just like with soft bounces, your data’s overall potential was decreased by 15%. On top of that, when your email service provider sees that you are using addresses that are incorrect and experiencing poor email deliverability, they will make the assumption that your email data quality is low. Each hard bounce will negatively impact your domain’s reputation thus impacting future email deliverability, so if you have a high bounce rate for long period you can do serious damage.

Bounce management

Making sure that your bounce rate stays low (lower than 5%) is very important for maintaining your domain reputation and keeping email deliverability and open rates high (between 40-70%).

So here are a few key things to remember:

  • Ask your data provider what the estimated bounce rate is (in hubsell’s case it is less than 5%) and if the bounce rate is too high consider another provider.
  • Monitor your campaigns and pause/stop the campaign if you’re hitting greater than a 10% bounce rate.
  • Make sure that bounces are recorded/marked correctly as sending a follow-up email to a bounced email is equally bad as sending the first email, and it is totally avoidable.

Sender’s email – kind of a big-deal if you want to have one-on-one conversations with your prospects

So let’s quickly look at the different settings which are possible (there may be more but they are not common).

Sender’s email setting types

  • You can send emails from a third party server which is typically the case with services like SendGrid and MailChimp etc.
  • You can send email from your outbox but under an alias, e.g. let’s say that my email address is ‘’ however I have an alias for outbound emails only which is ‘’ – keep in mind that aliases are not separate users in your email service provider setup, they are merely a different email address used by the same user.
  • You can send email from your primary mailbox.

Let’s discuss each one by one.

Third party server sending

While third party servers are valuable for use-cases such as newsletters to subscribers, massive mailings and e-commerce drip campaigns, they have limited usability in the world of cold outreach. There is a very good reason for that, cold outreach needs to be or at the very least seem to be one-on-one, a requirement that mass-mailers and third party senders cannot fulfill.

When you use a third party server to send your emails the details in your message indicate that it is mailed by and signed by certain domains.

Email Snippets for users

The information attached to the message is checked by the receiving server where it will give your message a rating. When the message is sent from a third party server the rating given to it is lower than when the message is sent from your mailbox directly. A low rating means a lower inboxing-rate, or conversely the higher rate means your message ends up in the spam folder.

Aliases vs unique mailboxes

An alias is an email that is not a separate user but rather shares the inbox of another mailbox, e.g. and can belong to the same person however one of them is the user and the other is an alias attached to the user. Alias email addresses are not considered as full mailboxes by the recipients servers, however not as detrimental as third party servers, they are still less ideal compared to your primary mailbox for doing cold outreach.

Your primary mailbox has many strong points, firstly it most likely has a longer history than your alias created for the sole purpose of doing cold mailings. Secondly, a primary mailbox has incoming mails from your colleagues, your prospects and your customers, so there is a bigger proportion of email traffic coming in comparison to an email that is created for the sole purpose of sending cold emails.

Recipients’ email – anything other than the direct corporate email address is a sub-par strategy

There are three main email types that you can target when doing your cold outreach:

Corporate email –
Role-based emails – marketing@ or info@
Private emails –

Every time you send an email I highly suggest you to target corporate emails.

Why role-based emails aren’t a good idea

Role-based emails are something both our customers and us don’t use because a lot of times these emails can be managed by more than one person. If you’re trying to target a specific decision maker and somebody else reads the email instead, it won’t be the best fit for them according to the dynamic placeholders that you used.

Also, this might increase the chances of your email getting a soft bounce, which, as we have seen before, is a metric that we want to keep as low as possible to keep our campaign potential high. To top it off, role based emails have too much noise because they are they easiest to be found and therefore receive a high volume of emails.

Why private emails aren’t a good idea

So, if role-based emails are not the ones we should use, then the next logical step would be to send the campaign to the target’s personal email. Unfortunately, this is not the best move either. First, let’s clarify what a personal email is: a personal email is the one that has attached an ending with a freemailer like @gmail, @yahoo, etc or on another paid/hosted server not meant for business. Usually private emails are free email accounts that the recipient might use for their personal affairs.

It’s never a good idea to email private email addresses because the recipients will feel very intruded upon, the content of your message is not relevant to them personally, and according to GDPR it is not legal in all countries in the EU.

Another deterrent from using personal emails is that when people are checking their private email, they are less likely to be in work mood, which can be for or against you. It can be for you due to them having lowered barriers which means they are more likely to open the email. However, it can be detrimental because their mind is not focused on work which means they might not even want to open your email and think about work.

And so, it comes down to one type of email: the corporate email.

Direct corporate emails are the way to go

Here at hubsell we always recommend our customers to target the corporate email of their recipient because it is the most productive of the three options and doesn’t come with the issues related to other two types of emails explained above.

Subject line – say in a few words in the subject line what you say in 100 words in your email and don’t do click-baiting

Some time ago I wrote an article on the kind of emails that end up in spam which I highly recommend reading in addition to the content in this article. In the current section ‘subject line’ and the next one ‘message copy’, I would like to tackle some of the key differentiators on ongoing basis after you’ve taken care of the data and technical set-up.

Let’s say that you did everything well. You’ve got excellent data, with only corporate direct email addresses, you’ve set-up your DMARC, DKIM/SPF properly, you’re using your own primary email do the outreach. All boxes checked with stellar ratings. You can mess it all up if you use bad subject lines (like shown in the blog post about email that end up in the spam folder).

Your goal with subject lines

Your ultimate goal when writing a subject line is to get the target to open the email, however with one caveat ‘do not trick or bait the recipient into opening your email’. If you use click-bait tactics to increase your open rate then you’re ‘inflating’ it without an increase in the value of those opens. If you remember at the start of the article I mentioned open to positive reply rate, this metric will decrease if you use click-bait tactics and your unsubscribe/spam reporting rate will go up.

A good subject line has to entice/welcome/encourage the recipient to open your email instead of other emails in their mailbox.

What to do and what not to do

Let’s get into the nitty-gritty.

    • There is a lot you can do with subject lines as long you remember the following:
  • Keeping the number of characters around 60 because most email clients will display between 40-70 characters on desktop and tables, and around 30-60 on smart phone screens
  • The character limit in email subject line includes the first n count of characters in the body of the email, i.e. if I have a subject of only 10 characters, then the first 30-60 characters of your email body will be visible in the preview snippet
  • In mobile phones (landscape or portrait view) the subject and body are on two separate rows so the length of the subject does not impact how much of the email body is visible to your recipient
  • Don’t use CAPS, exclamation marks ‘!’, or more than one question marks ‘?’ (one is okay)
  • Avoid spam words and phrases such as ‘free’, ‘money’, ‘risk free’, ‘apply now’ etc (the list is huge – and often times contextual)
  • Don’t use numbers or symbols e.g. #1
  • Don’t “FWD:” a prefix attempting to appear as if the email came from someone the recipient knows (check my comment on click-baiting)

Some things that I’m on the fence about, I don’t use them myself but some of our customers do and they get results, and some others don’t get results.

  • ellipses ‘…’,
  • Starting every word with a capital letter
  • Generic short subject lines such as ‘quick question’, ‘question’, ‘feedback’ etc.

How to go about writing a good subject line

There are few mental checkboxes you can mark when creating subject lines.

Number one is to ask yourself ‘does my subject line indicate what the email content is about and does it indicate that consistently.’ If it doesn’t you run the risk of misleading or creating clickbait subject line. Sounds simple, it really is not. It’s really hard to take what you said in about a 100 words and summarize it into 10 or so.

Number two is to check the length of your subject line, if it’s 10-20 characters then you need to take the first 20-50 characters of your email body as part of your subject line. Where if the subject line is long you’ll have less room to display the start of the message. See the images below for comparison.

email preview snippet on mobile phones

email preview snippet on desktop

So what you see is that on desktop, laptop, tablets your email subject and the start of the email body is on the same row, whereas on mobile phones (also landscape) is on two separate rows.

Static vs dynamic subject lines

Number three is figure out whether to make it personally relevant to the end recipient or not. And if yes (which I recommend) how and to what extent. Let me elaborate on that a little, personalization in the email subject line has been commonly limited to ‘static placeholders’ such as , , and etc. However there is another level which we, at hubsell, called ‘dynamic placeholders’ which use ‘if-this-then-that’ logic to enable personalization in a much deeper way.

Consider the following examples of static placeholder fitted subject lines:

  • Quick question about
  • , quick question about
  • , quick question about regarding your [your topic]

Most important thing you should remember is that like anything else in cold outreach personalization is key. A lot of marketers and sales developers fail because they limit themselves to static content.

Now consider these examples of dynamic placeholders fitted subject lines:

  • , // [your name], [your company name] – intro regarding {