The Two Metrics Marketers Often Confuse — and Why That’s a Problem

To understand why deliverability is important, it is important to first know the difference between “delivery” and “deliverability.” 

Email delivery refers to whether the ISP (Internet Service Provider) accepts the email a brand sends. This metric doesn’t distinguish between messages that land in an inbox, a spam folder, or a junk folder—only that they were accepted and didn’t bounce. The delivery rate simply reflects the percentage of emails that weren’t returned to the sender. 

Email deliverability, on the other hand, goes a step further. It focuses specifically on inbox placement — whether the message was actually delivered to the recipient’s inbox instead of being filtered into spam or junk. And that’s where the real impact happens. Messages that land in the inbox are more likely to be opened, clicked, engaged with, drive traffic, and convert — simply because they’re being seen.

Deliverability is a Real Success Measure 

Let’s say a company is consistently seeing a 97% delivery rate. Sounds great, right? But if open rates are dropping and engagement is low, there’s a good chance that the brand has a deliverability problem — and it’s quietly eating into performance. 

Inbox placement is influenced by various factors, but the common thread is engagement. 

What Factors Impact Email Deliverability

Below are six key factors that influence whether emails land in the inbox — or the spam folder:

1. Email Engagement: The most powerful indicator of deliverability. When users open, click, reply, or even move emails out of the spam folder, it boosts the sender’s reputation. When they ignore, delete, or mark them as spam — it does the opposite. 
2. Send Volume: ISPs look for consistency. Sudden spikes in volume can appear spam-like. That’s why gradual warm-ups and limiting increases to 2x or less is the best-recommended practice. 
3. Send Frequency: Bombarding subscribers with too many emails can backfire. Over-sending leads to complaints and disengagement, both of which hurt inbox placement. Brands must find the right cadence — and stick to it. Plus, it can cause Marketing Fatigue. 
4. Email Content: From subject lines to images and copy, content needs to feel relevant. Personalized, segmented messages increase engagement and signal to ISPs that the messages are wanted. 
5. List Quality: Where are the subscribers coming from? Has the brand recently validated its data? Invalid or dormant addresses lead to bounces, spam complaints, and low engagement, all of which raise ISP red flags. 
6. Sender Reputation: A brand’s sending domain and IP address have a reputation that builds over time. If it’s sending to poor-quality lists or hitting spam traps, ISPs will notice — and may block accordingly. 

ISPs Have Limited Vision 

ISPs use their own algorithms to determine whether messages are wanted or unwanted. They evaluate engagement across multiple campaigns, not just the latest one. If engagement drops — opens fall, deletions rise, complaints tick up — inbox placement will suffer. 

Even with a stable delivery rate, brands can see steady declines in openings, clicks, and conversions. That’s how deliverability issues chip away at marketing performance without being immediately obvious. 

Signs a Brand Might Have a Deliverability Problem

Below is a list of common red flags that suggest a brand’s emails aren’t reaching the inbox:

• A steady decline in unique open rates 
• Increasing bounce rates 
• ISP feedback showing blocked or throttled sends 
• Appearances on blacklists (global or ISP-specific) 
• Subscriber reports that messages are going to spam or disappearing entirely 

The INBOX Method to Improve Email Deliverability

A clear, memorable framework to fix problems, improve inbox placement, and protect sender reputation: 

• I – Identify & Suppress Inactive Users: Stop emailing contacts who haven’t engaged in the past 30 to 90 days. Reduce risk by focusing on active recipients. 
• N – Nurture Clean Lists: Clean your lists monthly, bi-monthly, or quarterly to remove invalid emails and prevent hard bounces. 
• B – Be Relevant and Personal: Use behavioral data and dynamic content to personalize messages. Better relevance equals better engagement. 
• O – Observe Key Metrics: Monitor opens, clicks, complaints, bounces, and blocks. Watch for dips in performance that signal trouble. 
• X – Exclude Cold or Unverified Lists: Avoid bulk uploads and cold outreach. Only message-verified, opt-in users to maintain trust and deliverability. 

In Summary 

Deliverability isn’t luck. It’s the result of smart, consistent practices — and a deep understanding of how ISPs reward (or penalize) senders. 

Brands can’t outsmart the system — but they can work with it. The key is to focus on real engagement, clean lists, and content the audience actually wants to receive. 

Don’t settle for “delivered.” Aim for inboxed — and engaged. 
 
For more insights on how to ensure email deliverability, contact us to request a demo.

Published on April 10th, 2025

Posted in

• Retail & eCommerce
• Email Marketing
• Personalization

Dana Carr

Dana Carr is Optimove’s Director of Email Marketing. Dana has over 20 years of experience managing the email marketing strategies of many recognizable global B2C and B2B brands. As the Director of Email Marketing, Dana is bridging the gap for Optimove’s customers by providing a data-driven marketing plan and timely implementation grounded in best practices, targeted content, and visually engaging design.