How to Unlock the Hidden Metrics of Email Deliverability

Nilam Oswal

Nilam Oswal

Senior editor

Parul Saxena

Chief editor

Last updated: May 20, 2021

Email marketing continues to remain a popular method of marketing. However, it is a tricky business. With so many filters, features and settings that come with email inboxes, it is easy for an email to get lost in transit and not make it to the intended recipient’s inbox at all. The whole exercise of email marketing becomes pointless in this scenario. That is not to say that email marketing cannot be successful. In order for your email marketing efforts to be a success, you must determine what needs to be monitored and measured. Email marketing is only as successful as its deliverability rate.

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The Hidden Metrics of Email Deliverability

Most email marketers are well-versed with metrics that indicate a campaign’s performance. These are typically metrics such as the open rate, the click-through rate, the conversion rate and also the unsubscribe rate. These are more or less, the standard metrics by which email marketing is usually measured. However, most email marketers are losing sight of the fact that to effectively make it to an inbox, engagement is key. 

All major email service providers track the positive or negative interaction that your subscriber has with your email communication to make filtering calculations that eventually determine where your emails must be placed. Marketers must, therefore, ask themselves how they can create a good experience for their subscribers. 

What are these hidden metrics? Why do email marketers seem oblivious to them? That is because, while reports provided by email service providers include standard metrics that most of us are familiar with, the reports remain silent of the metrics they actually use to filter emails.

Here are some of the hidden metrics that email service providers track, that you may have overlooked. Monitoring and measuring your email marketing strategy through these metrics might unleash the hidden potential of your email marketing program. By improving email engagement, marketers will not only see a higher ROI, but it will also help them protect their email marketing efforts.

Let us discuss what these metrics are,

1. Spam Placement Rate

There are largely two reasons why your emails would directly qualify as ‘spam’- your email was an obvious unsolicited bulk email or one of your previous emails was explicitly identified as spam by the recipient. The spam placement rate is nothing but the number of your emails that automatically go to the spam folder from the total number of emails sent. There are various factors that may cause email service providers to directly send your email to spam. Your email may contain content that is characteristic of spam emails, your sending patterns, and behaviors, or how a subscriber has previously interacted with your email communication. 

It is important to monitor and track your spam placement rates, as subscribers seldom open spam folders unless they are looking for a particular email that should have been in their inbox. If you have a low spam placement rate, it shows that your subscribers wish to receive your email and that you are a trusted sender. Monitoring and tracking the spam placement rate can also help you gauge the response to a new email marketing campaign. A sudden spike in spam placement rate could indicate an issue with your campaign.

2. Read Rate

This is more reliable than the standard open rate metric. While the open rate measures how many of your emails were opened, the read rate takes into consideration all the emails that were viewed regardless of the image rendering. When messages are ‘read’, it naturally means that a subscriber wishes to continue receiving your emails. Therefore, the read rate is the number of emails that were marked as ‘read’ from all that emails that you send. 

There are various factors that impact your read rate. All email marketers know how important timing is when sending an email and the impact a good subject line can have on recipients, ultimately leading them to read the email. A high read rate would indicate that your email marketing campaign is managing to generate subscriber interest. A low read rate would indicate that your campaign is failing to engage subscriber interest. Read rates can impact deliverability significantly. Consistently low read rates will eventually cause the email service provider to classify your communication as spam.

3. Ignore Rate

You might also call it the ‘Deleted Before Reading’ rate. If subscribers determine that your email is irrelevant to them or they do not wish to continue receiving them, they may simply delete the emails even before they open them. Therefore, this is the total number of unread emails that were deleted from all the emails that you sent. 

A high ignore rate can indicate various issues with your marketing program. It might show that your emails are unable to grab your subscriber’s interest. If there is a sudden rise in the ignore rate, it could indicate an issue with a recent campaign. A consistently high ignore rate could indicate that you did not take the subscriber’s permission before sending him or her emails. It could also indicate a general dissatisfaction with your overall email marketing strategy. A high ignore rate would eventually cause email service providers to believe that subscribers do not wish to receive your email which will definitely impact deliverability. 

4. Reply Rate

An absolute win for the email marketer, when subscribers reply to your email, it shows that you have managed to pique their interest. It also indicates that your email successfully conveyed a ‘personalized’ message. However, one cannot simply rely on numbers, as subscribers may be replying to your emails, asking you to take them off from your mailing list. The reply rate is the number of email replies received from the total number of emails sent.

More often than not, a high reply rate shows that your subscribers are happy to engage with you and wish to continue receiving your emails. Naturally, it would impact deliverability favorably. However, sometimes email marketers develop an overzealous approach and design their communication to solicit replies. This may be unnecessary. Also, it must be noted that email services providers do not expect subscribers to respond to emails, so a low reply rate will not impact deliverability negatively.

5. Forward Rate

Another indicator of high engagement, when subscribers forward your emails to others that may be interested, it not only shows that they want to continue receiving your emails, but it also serves as their endorsement of your marketing efforts. It means that your email was interesting enough for subscribers to think that their friends or family might think so too. The forward rate is the number of emails that were forwarded out of those that you sent. 

A high forward rate would indicate that your subscribers do not just find the content relevant for themselves, but also others in their network. A low forward rate will generally not have an impact on deliverability, as it is not typical subscriber behavior. 

6. Complaint Rate

All email service providers offer their users the option to explicitly mark or report an email as ‘spam’ or ‘junk’. Subscribers typically resort to this option when the email is unsolicited, irrelevant or even offensive. The complaint rate is, therefore, the number of emails that are marked as spam or junk out of the total number of emails sent.

Anyone with even a basic knowledge of how email works know what a setback a high complaint rate can be to your email marketing program. By reporting an email, a subscriber makes it clear that your email is unwanted. Such complaints are taken very seriously by email service providers while filtering emails. Being reported as spam/junk even once by a subscriber will most probably lead to that subscriber never seeing an email from you in his/her inbox again. 

7. ‘This Is Not Spam’ Rate

Sometimes people do check their spam folder to ensure that they have not missed any emails that should have been delivered to their inbox. Email service providers give them the option to choose “This Is Not Spam” or “Not Junk” so that such emails are not automatically sent to the spam folder in the future but are delivered to the inbox. It is a clear signal to mailbox providers that subscribers wish to receive such emails.

The ‘This Is Not Spam’ rate is the number of times your email was marked so, by subscribers out of the total emails sent. It is also known as the ‘rescue rate’, alluding to how many of your email messages were ‘rescued’ from the spam/junk folder by a subscriber out of the total number of emails sent.

We have already discussed what can contribute to a high spam rate. If you do have a high spam rate, a low ‘This Is Not Spam’ rate would indicate that you have not sought permission from your subscribers, there is little awareness about your brand or even a lack of interest from the subscriber. A high ‘This Is Not Spam’ rate serves as a great validation for email marketers, as it shows that your email was important enough for your subscribers to go looking for them and then retrieve them.

Optimizing Your Email Marketing Strategy

In light of these metrics, it cannot be denied that engagement is crucial to the success of email marketing. Marketers must strive to increase positive engagement in the form of reading rates, replies, forwards, etc. and curb negative engagement indicated by spam complaints and messages that are deleted before reading. 

  • Test: Sure, you may have an attractive email with the perfect subject line, but it still does not guarantee engagement. To be sure, you can test the emailers on a small sample from your mailing list and make data-driven decisions.
  • Segment: Not all consumers are alike. Organize your mailing list. Identify the tastes and preferences of your subscribers. Segment them and tailor your communication in a manner that resonates with them the most. 
  • Clean: Most mailing lists have subscribers that do not positively or negatively engage with your emails. They are often classified as neutral. However, they may simply be ignoring you. There is no point in crowding your mailing list with people who do not want to receive your emails. Check whether you have correct email addresses and remove inactive addresses from your list from time-to-time.


Email marketing can be complex but very rewarding. However, the importance of email deliverability cannot be undermined. For any email marketing program to be successful, marketers must first and foremost ensure that their emails are reaching their subscribers. It is important to know what to measure. A strong set of metrics is therefore crucial. 

Nilam Oswal
Nilam Oswal is a Content Marketing Head and Brand Strategiest at SoftwareSuggest. When she's not hard at work, she can be found wandering, reading, and just generally having a good time in life.

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