Email Deliverability Best Practices

What happens when a well-crafted email campaign NEVER lands in your subscribers’ inboxes?

In an email campaign, you put a lot of effort into drafting the perfect copy. A subject line to pique curiosity. Strong content and creative designs to capture the attention. But none of this matters if the email lands in the spam folder. 

If that happens, email performance can drop drastically, and campaigns can lose visibility. The issue, however, might not be the campaign itself. It is email deliverability. This is exactly the kind of problem an email deliverability consultant is trained to diagnose. 

But before you consider bringing in expert help, it helps to understand what deliverability actually is and what’s working against you

What is Email Deliverability?

Email deliverability reflects the relationship between your sending behavior and how mailbox providers evaluate it. This invariably affects the inbox placement of your email in the receiver’s inbox. This evaluation also tells the inbox providers whether your customers actually want the emails you’re sending or not.

A strong engagement between the sender and the receiver solidifies your sender reputation and improves the chances of your messages actually reaching the right inbox. 

Let’s look at some factors that affect email deliverability (and inbox placement). 

Factors That Affect Email Deliverability

Email deliverability is not governed by a single variable. Instead, it reflects the cumulative impact of authentication, sending infrastructure, subscriber acquisition practices, engagement signals, and long-term reputation management. 

Mailbox providers continuously evaluate these signals to determine whether a sender is legitimate or a potential source of unwanted mail.

Other key factors that can affect email deliverability are – 

• Email marketing infrastructure – With proper authentication (SPF, DKIM, and DMARC), mailbox providers verify legitimate sender email addresses. 
• Sending volume and consistency – Any irregular sending pattern or sudden spike can trigger spam filters. 
• Email content – Subject lines and email formatting can influence spam filtering decisions. 
• Spam complaints and bounces – High complaint rates and invalid email addresses are one of the most common reasons that weaken sender reputation. 
• Subscriber engagement – Opens rates and click rates show whether recipients value your emails. 
• IP and domain reputation – Mailbox providers review the historical reputation of your sending IP addresses and domains when deciding on your inbox placement. 

Best Practices to Improve Your Email Deliverability

So, how do you make sure that your emails are consistently reaching the inbox? 

While inbox placement ultimately rests with mailbox providers, senders are far from powerless. Over time, mailbox providers have established a set of proven practices that significantly improve the probability of successful inbox placement. 

As we established before, several factors affect email deliverability. But the good news is that most delivery failures can be prevented. When senders establish a well-configured sending infrastructure and meet the other requirements, mailbox providers develop confidence in the legitimacy of their email programs. 

In the section below, we are going to define some practices that many email marketing agencies (like InboxArmy) trust to maintain consistent inbox placement. 

1. Authenticate your email domain

We can’t stress enough how important authentication forms are. They are the foundation of deliverability systems. Before mailbox providers evaluate engagement signals or sender reputation, they first verify that the sender is authorized to transmit mail on behalf of the domain in question.

There are three authentication methods for this verification process – 

• Sender Policy Framework or SPF allows domain owners to declare which mail servers are authorised to send messages using their domain. Mailbox providers validate incoming messages against the domain’s published SPF record. 
• DomainKeys Identified Mail, or DKIM, is a cryptographic signature added to each email. This signature is a confirmation that the content has not been altered in transit and is another source of verification. 
• Domain-based Message Authentication, Reporting, and Conformance, or DMARC, builds upon SPF and DKIM by allowing domain owners to define policies for messages that fail authentication checks. It also generates reporting data that helps senders monitor authentication performance and detect potential spoofing attempts.

If these authentication requirements are not met, then your messages are far more likely to be filtered or rejected before they reach the desired inbox. 

2. Maintain a Stable Sending Infrastructure

Sending infrastructure plays a critical role in deliverability. High-volume senders often use dedicated IP addresses to establish an independent reputation, rather than relying on shared IP pools. 

Because new IPs lack sending history, they must be gradually warmed up so mailbox providers can observe consistent engagement and build trust in the sender.

Now, if there is a sudden spike in sending volume from an unfamiliar IP address, it often resembles spam activity. And as a result, mailbox providers may temporarily limit or block delivery until the sender has established a credible sending history with the right authentication. 

3. Implement a Responsible Opt-In Process

Deliverability outcomes often trace back to how email addresses were originally acquired.

When subscribers knowingly request to receive messages, engagement tends to remain high, and complaint rates remain low. Conversely, sending messages to individuals who did not explicitly consent to receive email frequently results in spam complaints, unsubscribes, and negative engagement signals.

For this reason, many senders implement double opt-in subscription processes. Under this model, a subscriber must confirm their subscription through a verification email after submitting their address. 

This additional step helps eliminate – 

• Mistyped email addresses
• Automated bot signups
• Low-intent or accidental subscriptions

Although double opt-in may slow the rate of list growth, it typically produces a more engaged audience. 

4. Maintain a Clean and Healthy Email List

List quality can make or break your email deliverability performance. 

Any company generally has an email database that can accumulate inactive subscribers or abandoned email addresses. If you continue to send your email campaigns to these contacts, then it could result in low engagement metrics and increased bounce rates. This is interpreted as unwanted by mailbox providers. 

If you want to maintain list hygiene, you could –

• Remove invalid or bouncing email addresses
• Identity and remove long-term inactive subscribers
• Run periodic re-engagement campaigns
• Monitoring subscriber activity trends

Many mature email programs have a suppression strategy that automatically excludes contacts who have not engaged with emails within a defined period. 

5. Avoid Spam Traps

If you are from the email marketing industry, you must have come across email addresses used by internet service providers and anti-spam organisations to catch unauthorised senders. It is a way to identify senders who ignore responsible list management practices.

These addresses do not belong to real subscribers. Instead, they exist solely to detect senders who rely on purchased lists, scraped databases, or outdated contact records.

If a sender repeatedly comes in contact with spam traps, then mailbox providers interpret this activity as evidence of not maintaining list hygiene. Thus, there’ll be a decline in sender reputation. 

The most effective way to avoid spam traps is simple – only email people who actually asked to hear from you. Stick to permission-based signups, and make it a habit to clean your list by removing inactive or outdated contacts.

6. Craft Email Content That Encourages Engagement 

Even though spam filters today pay close attention to how people interact with your emails, the content you send still matters a lot for getting into the inbox.

If your subject line is packed with exclamation marks, makes promises it can’t keep, or feels overly salesy, people notice, and not in a good way. When subscribers feel tricked, or the message doesn’t match their expectations, they’re far more likely to ignore the email or hit the spam button.

Instead, the best recommendation is to keep things simple. Something that actually delivers value. 

So, create an email that respects the reader. The subject line should say what the email actually delivers. The message should be what the subscriber signed up for. But content alone won’t decide whether or not your email reaches the inbox. It does strongly influence engagement, though. 

7. Encourage Positive Subscriber Engagement

Mailbox providers pay close attention to how recipients interact with your emails. When people do any of the following, it signals toward a welcome and relevant communication – 

• Open messages
• Click links
• Reply
• Move emails out of spam
• Add the sender to their contacts

At the same time, when emails are consistently ignored or deleted without being read, it sends the opposite message. Over time, this lack of engagement can weaken a sender’s reputation and increase the likelihood that future emails will be filtered into the spam folder. 

In other words, strong deliverability is an amalgamation of proper technical setup and sending emails people actually want to receive. 

8. Monitor the Deliverability Metrics Continuously 

Email deliverability isn’t something you set up once and forget. You need to watch it, measure it, and gradually improve it over time. 

That’s why the best email teams keep a close eye on a few metrics. These numbers tell you whether your program is healthy or if something needs attention. 

Here are the metrics you need to keep an eye on – 

• Bounce rate – If this number is high, it usually means your list contains invalid or outdated email addresses.
• Spam complaint rate – When recipients mark your emails as spam, mailbox providers start losing trust in your sending behavior.
• Open and click rates – These show whether subscribers actually find your emails interesting enough to engage with.
• Inbox placement rate – This tells you how many of your emails are actually reaching the inbox instead of getting filtered into spam.

Begin consistently tracking these signals, and you will be able to catch the problems early and make the required adjustments in your email campaigns. 

9. Implement a Sunset Policy for Inactive Subscribers

Inactive subscribers might seem harmless, but they can quietly damage your deliverability. 

When a big chunk of your list stops opening or clicking your emails, then it is assumed they aren’t wanted. And a lack of engagement affects sender reputation. 

This is where the sunset policy comes in. A sunset policy is the process of identifying subscribers who have not interacted with your emails for a certain period of time and gradually removing them from your mailing list. Most sunset policies follow a simple process – 

• Set an inactivity threshold, like no opens or clicks for six months.
• Then, send a re‑engagement campaign asking if they still want to hear from you.
• If they still remain inactive, suppress or remove them from future sends.

Focus your email campaigns on subscribers who actively engage with your emails. This will keep the engagement metrics strong and send a clear positive message to mailbox providers. 

If you’re reading these solutions, it’s probably because you’ve encountered these email deliverability challenges, and that is normal. Even the most experienced teams have probably encountered it multiple times. Filters change, algorithms evolve, and sometimes emails that used to land in the inbox suddenly don’t. Figuring out why that’s happening usually takes a closer technical look.

And this is where InboxArmy comes in. We help brands uncover hidden deliverability issues and put the right practices in place. The next section will show you how we helped some brands increase email deliverability. 

Real-World Examples – How Deliverability Improvements Drive Results

The following examples illustrate how structured deliverability remediation can restore your sender reputation and ultimately improve email deliverability. 

Case Study – Rebuilding Domain Reputation for Zinch

When Zinch started its email program, its domain reputation was already struggling. They had a large contact list (over 81,000 records) but no real insight into how healthy that data actually was. 

So the first step was relatively simple – slow everything down and diagnose the problem. 

We started with small sends and immediately saw the problems. Bounce rates ranged between 2–6%, which is far above healthy levels. Digging deeper, we found that Yahoo addresses were causing major bounce problems because many inactive accounts were returning false “valid mailbox” signals.

Once those addresses were removed and the list was cleaned again, we implemented a structured domain warm-up. We began sending only to the highest-quality contacts and gradually expanded the audience as engagement signals improved.

And with time, mailbox providers started trusting the domain again. 

Here are the results after 5 months – 

• Domain reputation improved from Bad → High
• Bounce rate dropped from 10% → 0.55%
• Open rates reached around 40%
• CTOR reached 60%

In short, once the data was cleaned and the domain was warmed properly, deliverability automatically followed. 

Read more: https://www.inboxarmy.com/email-marketing-casestudy/zinch/

Case Study: Anywhere Real Estate – Restoring Inbox Placement

Another study where we helped a brand increase email deliverability is with Anywhere Real Estate. Anywhere was facing a different problem. Their email program had been losing inbox placement for months, and no one could clearly explain why. 

Their open rates had dropped before 5%, and their domain reputation had fallen. In fact, their team had even created a new sending domain to try to solve the issue. 

But the new domain wasn’t performing either. 

When we ran a full deliverability audit, the problem became clear – 

• SPF authentication was misaligned
• Bounce rates were unusually high
• Spam complaints were increasing
• Sending volumes were inconsistent

This problem required a structured cleanup. 

So, first, we cleaned and validated the contact database. Then we corrected authentication issues, implemented proper suppression rules, and rebuilt the sending pattern using a controlled domain warm-up strategy. 

We started sending only to high-quality contacts and increased volume gradually while monitoring mailbox provider responses. 

The results we achieved were as follows – 

• Domain reputation improved from Low → High
• Inbox placement rose from the low 60% range
• Bounce spikes disappeared
• Spam complaints stabilized
• Open rates increased from below 5% to 20–40%

Once the technical issues were fixed and the sending pattern became consistent, mailbox providers started trusting the domain again. 

Read more: https://www.inboxarmy.com/email-marketing-casestudy/anywhere-a-real-estate-company/

These examples highlight an important truth about deliverability – when something breaks, it is not random. There is always a technical, data-based, or sending-behavior issue behind it.

Conclusion

Email marketing only works if your emails actually reach the inbox. If they’re landing in spam or getting blocked, even the best campaigns won’t perform.

Deliverability comes down to a few key things – proper authentication, clean data, consistent sending, and strong engagement. When those signals are healthy, mailbox providers trust you and your emails reach subscribers where they’re supposed to.

The good news? Most deliverability problems can be identified and fixed once you know where to look. And InboxArmy can help you with that. 

Schedule a free consultation with our email marketing agency and start improving your email deliverability today.

Frequently Asked Questions

What is the best way to improve email deliverability?

Start with the basics. Make sure your domain authentication (SPF, DKIM, DMARC) is set up correctly, send only to people who actually opted in, and keep your list clean. Consistent sending and strong engagement signals tell mailbox providers your emails belong in the inbox.

How long does it take to improve email deliverability?

It depends on the problem. Some fixes, like authentication issues, can improve deliverability quickly. Reputation recovery or domain warm-up takes longer. In most cases, meaningful improvements appear within a few weeks to a few months.

Can I fix poor deliverability by switching email service providers?

Usually, no. Changing ESPs rarely fixes the root issue. Mailbox providers track your domain reputation and sending behavior, not just the platform you use. If the underlying problems remain, deliverability issues will follow you.

How often should I clean my email list?

List hygiene should be ongoing. Review your data regularly, remove invalid addresses, and suppress subscribers who haven’t engaged in months. Most mature programs run list-cleaning or re-engagement checks every few months to protect sender reputation.