The ultimate guide to inbox placement

Why it matters and how to consistently reach the inbox

Email teams spend a lot of time optimising what happens after an email is opened. Subject lines, copy, design, calls to action. All important work. But there is a more basic question that often goes unanswered: did the email actually reach the inbox?

Inbox placement is the difference between an email that is technically delivered and an email that is actually visible to the recipient. And that difference matters more than many teams realise. An email that lands in spam might as well not exist, no matter how well written it is.

Before we start: A common misconception is that secondary tabs, like Gmail’s Promotions tab, are not the inbox. Even though many marketers equate this to being sent to spam, it simply is not. These tabs are the inbox, just categorised.

This guide focuses on inbox placement as a practical, measurable part of your email setup. Not as a vague deliverability concept, but as something you can understand, calculate, test, and improve. We will explain what inbox placement really means, how mailbox providers decide where your email goes, how to measure your inbox placement rate, and what you can do to improve it over time.

The guide is written for teams sending transactional, system, and API driven emails, as well as marketers who want more reliable performance from their email programmes. You do not need to be a deliverability expert to follow along. We will keep the language simple, the examples concrete, and the advice actionable.

By the end, you should have a clear view of your current inbox placement, the risks that affect it, and the role your email infrastructure plays in protecting it.

What inbox placement really means

Inbox placement is often mentioned alongside email deliverability, but the two are not the same. Understanding the difference is the first step to improving how your emails perform.

Inbox placement vs email delivery

Email delivery is a technical outcome. It means that the receiving mail server has accepted your message. From a system point of view, the email is no longer bouncing and the send was successful.

Inbox placement is what happens next.

Once an email is accepted, mailbox providers decide where it should be placed. That can be the inbox or the spam folder, or in any secondary tab/folder. Inbox placement describes this final destination.

This distinction matters because delivery is binary. An email is either delivered or it is not. Inbox placement is not. Two emails can both be delivered successfully, but one appears in the inbox while the other is filtered out of sight.

A common example is a transactional email such as an order confirmation. The email is delivered, your system logs show success, but the customer never sees it because it landed in spam. From a technical perspective, nothing failed. From a user perspective, everything did.

For teams that rely on email for critical communication, delivery alone is not enough. Inbox placement is the metric that tells you whether your emails are actually reaching people.

Inbox, spam, promotions and tabs

After delivery, emails can end up in several different locations. The exact labels vary, but the principle is the same across mailbox providers.

Most emails aim for the primary inbox. This is where users expect important and time sensitive messages to appear. Other emails may be placed in secondary tabs or filtered views. These are still delivered, but they compete for attention and are often checked less frequently. Below is an example of a Gmail inbox:

Finally, emails can be sent to the spam folder. Messages placed here are actively hidden and are unlikely to be read at all.

From a sender’s perspective, only inbox placement offers reliable visibility. Even well intentioned emails can lose impact if they are filtered away from where users actually look. That is why inbox placement is treated as its own metric, separate from delivery.

Why inbox placement matters more than opens

For a long time, open rates were used as a proxy for inbox performance. If people opened emails, they must have reached the inbox. That assumption no longer holds.

Privacy features, image blocking, and automated opens have made open rates less reliable. An email can register an open without ever being seen, or be seen without registering an open.

The open rate has long been a topic of debate in the email marketing industry. Often dubbed a ‘vanity metric’, opens are influenced by a lot of factors, even robots. Read more about bot opens & clicks in our blog »

Inbox placement shifts the focus back to access rather than interaction. It answers a simpler and more stable question: did the email reach a place where the recipient could realistically see it?

This is especially important for transactional and system emails. A password reset or invoice does not need to be opened to be successful, but it does need to arrive in the inbox. Inbox placement gives you a clearer view of whether your email setup supports that goal.

Why inbox placement is critical for transactional and API emails

Transactional emails are often treated as inherently safe. They are expected, relevant, and triggered by user actions. But mailbox providers do not automatically trust them.

Transactional emails are not immune

Order confirmations, account alerts, password resets, and invoices can all end up outside the inbox. When that happens, the impact is immediate. Customers think their order failed. Users cannot access their account. Support teams receive tickets for issues that are not product related at all.

From the mailbox provider’s point of view, transactional emails are still emails. They are evaluated based on sender reputation, authentication, consistency, and behaviour. The fact that an email is important to you does not guarantee inbox placement.

This is why teams sometimes see strong inbox placement for marketing emails, but poor placement for transactional traffic sent through a different system or IP.

A common misconception is that a dedicated IP will help your deliverability and inbox placement, but this is rarely ever the case. Stick to best practices, but don’t assume you can handle everything yourself through a dedicated IP. Interested in learning why? Read Nick’s blog »

Inbox placement and customer trust

When transactional emails do not arrive as expected, trust erodes quickly. Users blame the brand, not the mailbox provider.

Missed confirmations and delayed notifications create friction at moments that matter. These moments often sit close to conversion, onboarding, or payment. Poor inbox placement turns email into a source of doubt instead of reassurance.

Over time, this leads to higher support costs, lower satisfaction, and unnecessary churn. Inbox placement is therefore not just a deliverability concern. It is a customer experience issue.

Why infrastructure choices matter more for transactional email

Transactional and API driven emails rely heavily on the underlying sending infrastructure. They are often sent from applications, triggered in real time, and scaled automatically.

This makes consistency, authentication, and reputation management even more important. Sudden traffic spikes, or mixed email types can all harm inbox placement.

Teams that treat transactional email as a core system component, rather than an afterthought, are better positioned to protect inbox placement over the long term. The platform and setup you choose play a significant role in how mailbox providers perceive your email traffic.

How the team at DPD put delivery at the core

By using Spotler SendPro, DPD no longer has to worry about the delivery of important emails. They know their emails are quickly delivered where they belong, just like their packages.

Read the DPD study

How inbox placement works behind the scenes

Inbox placement is not decided by a single rule or filter. It is the result of many signals that mailbox providers evaluate every time you send an email. Understanding these signals helps you make better decisions, even if you never see the full scoring process.

How mailbox providers decide where your email goes

When an email is sent, the receiving mail server runs a series of checks before deciding what to do with it. These checks happen quickly and automatically.

First, the provider verifies whether the sender is who they claim to be. This is where authentication comes in. Emails that fail these checks are more likely to be rejected or filtered.

Next, the provider looks at the sender’s past behaviour. This includes how often emails are sent, how consistent the volume is, and how recipients have interacted with previous messages.

Finally, the content and structure of the email are reviewed. This does not mean every word is analysed, but patterns are recognised. Layout, formatting, links, and overall structure all contribute to how the email is classified.

Based on these combined signals, the provider decides whether the email belongs in the inbox, a filtered view, or spam. This decision can differ per sender, per recipient, and over time.

Key signals that influence inbox placement

While the exact weighting of signals is not public, most mailbox providers rely on a similar set of indicators.

Sender authentication
Authentication proves that your domain and sending systems are authorised to send email. Proper configuration of SPF, DKIM, and DMARC reduces uncertainty and builds trust over time.

Sending history and consistency
Mailbox providers prefer predictable senders. Sudden spikes in volume, long periods of inactivity followed by bursts, or frequent changes in sending patterns can hurt inbox placement.

Even though spikes in volume are potentially penalised, mailbox providers understand seasonality too. Some of our customers send a higher volume during the summer period without issues. Balance is key.

Recipient engagement
How recipients interact with your emails matters. Emails that are read, kept, or replied to send positive signals. Emails that are ignored or deleted immediately can have the opposite effect.

Complaints and bounces
Spam complaints and high bounce rates signal poor list quality or unwanted email. Even small increases can have a noticeable impact on inbox placement.

Content and formatting
Clean HTML, accessible layouts, and clear structure help mailbox providers understand your email. Overly complex or inconsistent templates can trigger filtering, even without obvious spam content.

Each signal on its own rarely decides inbox placement. It is the combined pattern that matters. You’ll notice that inbox placement factors and deliverability best practices have some overlay, but there are some key differences. This recent study by Oracle tells you how deliverability best practices have changed over the years.

The role of sender reputation

Sender reputation is the result of your past performance as an email sender. It is built gradually and evaluated continuously.

Reputation is typically associated with your sending domain and IP addresses. This means that problems in one type of email can affect others if they share the same reputation.

A strong sender reputation makes inbox placement more resilient. A weak or damaged reputation makes every send riskier, even if the email itself looks fine.

This is why inbox placement should be managed as a long term process, not a campaign level fix.

How to calculate your inbox placement rate

Inbox placement sounds abstract, but it can be measured. The key is understanding what you are measuring and what the numbers do and do not tell you.

What inbox placement rate actually measures

Inbox placement rate shows the percentage of delivered emails that land in the inbox, rather than being filtered to spam or other folders. In simple terms, it answers this question: out of all the emails that were accepted by mail servers, how many reached the inbox?

This makes it different from delivery rate, which only measures acceptance, and from open rate, which depends on tracking and user behaviour. Inbox placement rate focuses purely on visibility.

The basic formula for inbox placement rate

The calculation itself is straightforward:

Inbox placement rate is the number of emails placed in the inbox, divided by the total number of delivered emails, multiplied by one hundred.

To calculate this, you need to know where delivered emails actually landed. Standard email analytics do not provide this information, which is why additional testing methods are required.

It is important to note that emails placed in spam or filtered views are still counted as delivered. They simply do not count towards inbox placement.

Why you cannot measure inbox placement with standard analytics

Most email platforms report delivery, opens, clicks, and bounces. They do not report inbox placement. This is because mailbox providers do not share folder level placement data with senders. Whether an email landed in the inbox or spam is only visible from the recipient’s side.

Open rates are often used as a proxy, but they are unreliable. Opens can be triggered automatically, and the absence of an open does not mean the email was filtered.

Inbox placement requires controlled testing, typically using seed mailboxes or monitoring tools that simulate recipient behaviour.

Common mistakes when measuring inbox placement

One common mistake is testing once and assuming the result is permanent. Inbox placement changes over time and should be monitored regularly. Another mistake is relying on small sample sizes. Testing too few mailboxes can give a distorted view of performance.

Finally, many teams mix different types of email in a single test. Transactional, marketing, and system emails behave differently and should be measured separately. Accurate inbox placement measurement requires consistency, patience, and a clear understanding of what the data represents.

Tools and methods to test inbox placement

Because mailbox providers do not share inbox placement data directly, measuring it requires indirect methods. These methods are not perfect, but they provide enough insight to identify risks, trends, and improvements over time.

Seed list testing explained

Seed list testing is the most common way to measure inbox placement.

A seed list is a controlled set of test email addresses spread across different mailbox providers. When you send an email to this list, you can log into each mailbox and see where the email landed.

By repeating this process consistently, you can estimate how often your emails reach the inbox versus being filtered to spam or other folders.

Seed testing works best when:

• The same templates are tested regularly
• Tests are run at consistent volumes
• Transactional and marketing emails are tested separately

The goal is not to get an exact percentage that applies to every recipient. The goal is to identify patterns and changes that indicate whether inbox placement is improving or declining.

What inbox placement tests can and cannot tell you

Inbox placement tests are directional, not definitive.

They can show:

• Whether emails are generally landing in inboxes or spam
• Differences in placement between providers
• Sudden changes after configuration or content updates

They cannot show:

• Individual user level behaviour
• Long term reputation impact on real recipients
• Engagement driven placement differences

This means inbox placement testing should be used alongside other signals, not in isolation.

How often you should test inbox placement

Inbox placement should be tested regularly, but not obsessively.

For teams sending high volumes or critical transactional emails, weekly testing is often appropriate. For lower volume or more stable setups, monthly testing may be enough. Another approach would be opportunistic, where you look at inbox placement when you see a drop in confirmed opens and/or engagement.

Testing is especially important after:

• Infrastructure changes
• Authentication updates
• Template redesigns
• Volume increases

The most common inbox placement problems

Inbox placement issues often feel sudden, but they usually have clear underlying causes. Recognising common patterns helps you respond faster and avoid repeating mistakes.

Authentication issues

Missing or misconfigured authentication is one of the most frequent causes of poor inbox placement.

When SPF, DKIM, or DMARC records are incorrect or incomplete, mailbox providers cannot reliably verify the sender. This increases filtering, even if the email content is legitimate.

Authentication issues often appear after:

• Domain changes
• New sending systems
• Vendor migrations
• DNS updates

Because these changes happen outside email tools, problems can go unnoticed for weeks.

Sudden drops in inbox placement

A sudden drop in inbox placement is usually linked to a change in behaviour rather than content.

Common triggers include:

• Large increases in sending volume
• Sending after long periods of inactivity
• Combining different email types on one sending identity
• Changes in sending timing

Mailbox providers react strongly to unexpected behaviour. Even positive changes, like growth, can cause short term placement issues if not managed carefully.

Good content, bad placement

Many teams assume that inbox placement problems are caused by wording or design. In reality, content is often not the primary issue.

Emails with clean copy and simple layouts can still be filtered if the sender reputation is weak or inconsistent. Fixing content without addressing infrastructure rarely solves the underlying problem.

This is why inbox placement should be treated as a system level concern, not just a copywriting task.

Transactional emails going to spam

Transactional emails are especially vulnerable when they share sending infrastructure with promotional traffic.

If marketing emails generate complaints or low engagement, that reputation can affect transactional messages sent from the same domain or IP.

Separating transactional and marketing traffic is one of the most effective ways to protect inbox placement for critical emails.

How to improve your inbox placement step by step

Improving inbox placement is rarely about one single change. It is about reducing risk, increasing trust, and keeping your sending behaviour predictable over time. The steps below focus on the areas that have the biggest impact.

Step 1: Get authentication right

Authentication is the foundation of inbox placement.

At a minimum, your sending domain should have valid SPF and DKIM records, and a DMARC policy that aligns with them. These records tell mailbox providers which systems are allowed to send email on your behalf and how to handle messages that fail checks.

Authentication should be:

• Complete across all sending systems
• Consistent for each email type
• Monitored after changes

Even small misalignments can reduce trust. When in doubt, simpler and stricter authentication usually performs better than partial or loosely configured setups.

With SendPro’s domain wizard, you don’t have to think twice about your authentication.

Step 2: Separate transactional and marketing traffic

Transactional and marketing emails serve different purposes and generate different engagement signals.

When both types are sent from the same domain or IP, poor performance in one can affect the other. This is especially risky for transactional emails, which users expect to receive instantly and reliably.

Separating traffic allows each stream to build its own reputation. It also makes inbox placement issues easier to diagnose and fix. For many teams, this step alone leads to noticeable improvements.

Use SendPro for your transactional email streams – and use Spotler’s email marketing functionalities for your marketing efforts!

Step 3: Build and protect your sending reputation

Sender reputation is built slowly and damaged quickly. To protect it:

• Increase volume gradually
• Avoid long gaps followed by spikes
• Keep sending patterns predictable
• Remove invalid addresses early

Reputation building is not a one off task. It requires ongoing attention, especially as products grow and sending behaviour evolves.

Step 4: Design emails for deliverability

Emails that are easy to read are also easier to classify.

Simple layouts, clean HTML, and accessible structure help mailbox providers understand your intent. Overly complex designs, excessive tracking elements, or inconsistent templates increase filtering risk.

For transactional emails, clarity is more important than creativity. Focus on content hierarchy, readable text, and predictable formatting.

More engagement with your emails means a higher chance of getting to the inbox. Use SendPro’s email template designer and follow best practices »

Step 5: Monitor engagement and feedback loops

Engagement acts as a signal of relevance. While transactional emails are not always opened, patterns still matter. Repeated deletes without reading, spam complaints, or ignored emails can all affect reputation.

Where available, feedback loops and monitoring tools help you spot issues early. Treat these signals as indicators, not accusations, and adjust before problems escalate. SendPro helps you gain these insights.

Inbox placement best practices for API and system emails

API and system driven emails behave differently from scheduled campaigns. They are triggered by events, sent in real time, and often scaled automatically. This makes inbox placement both more important and more fragile.

Why API based sending changes the equation

With API sending, volume and timing are controlled by your application, not your email tool.

This means that bugs, retries, or unexpected user behaviour can cause sudden spikes in traffic. Without safeguards, these spikes can look suspicious to mailbox providers.

API based sending requires tighter control over rate limiting, retries, and error handling to protect inbox placement. Discover how that works.

Dynamic content and attachments without hurting placement

Many system emails include personal data, dynamic fields, or attachments such as invoices and tickets.

To reduce risk:

• Keep attachment sizes reasonable
• Use consistent file types
• Avoid unnecessary formatting complexity
• Ensure dynamic fields are always populated

Broken personalisation or malformed attachments can trigger filtering, even when the message itself is expected.

Reliability and uptime as a deliverability factor

Mailbox providers reward consistency. If your sending system is unreliable, messages may be delayed, retried, or sent in bursts. These patterns can harm inbox placement over time.

Reliable infrastructure helps ensure:

• Predictable sending behaviour
• Stable authentication
• Consistent reputation signals

For system emails, deliverability is not just about content. It is about the dependability of the entire sending setup.

How the right sending platform supports inbox placement

Inbox placement is influenced by many factors, but some of the most important ones sit at platform level. The tools and infrastructure you use shape how mailbox providers experience your email traffic over time.

What to look for in a transactional email solution

A strong transactional email solution supports inbox placement by design, not as an afterthought.

Key characteristics to look for include:

• Clear separation between transactional and marketing traffic
• Strong support for authentication and domain alignment
• Predictable sending behaviour, even at scale
• Monitoring and logging that help diagnose issues quickly
• An API that allows control without encouraging risky patterns

The goal is not to optimise individual emails, but to create a stable environment where good inbox placement can be maintained as volume and complexity grow.

When switching platforms can improve inbox placement

Inbox placement issues are not always caused by the current platform, but there are situations where switching makes sense.

These include:

• Transactional and marketing emails sharing the same reputation
• Limited control over authentication or sending behaviour
• Poor visibility into delivery and errors
• Infrastructure that does not scale predictably

In these cases, improving inbox placement often requires structural change, not incremental tweaks.

Inbox placement checklist

This checklist can be used as a quick assessment or a recurring review.

Quick self assessment

Ask yourself:

• Are all sending domains fully authenticated?
• Are transactional and marketing emails separated?
• Is sending volume predictable and consistent?
• Do we test inbox placement regularly?
• Can we spot issues before users report them?

If several of these answers are uncertain, inbox placement is likely at risk.

Ongoing habits that protect inbox placement

Inbox placement improves when it is treated as an ongoing process.

Helpful habits include:

• Reviewing authentication after any system change
• Monitoring sending patterns as products evolve
• Testing inbox placement on a regular schedule
• Keeping transactional templates stable and simple

Small, consistent actions are more effective than reactive fixes.

Frequently asked questions about inbox placement