From Spam Folder to Inbox: Mastering Email Deliverability Basics

It can be really frustrating when you realize your emails are being reported as spam. Because no matter how hard you’ve worked, it all goes to waste if your emails don’t reach the inboxes. 

Mastering email deliverability is now essential, and no longer optional—an ROI of $36 ROI per $1 spent is very valuable for businesses. With poor deliverability, you will not get a share of that revenue pie.

The thing is, email deliverability isn’t just about creating emails and hitting ‘Send.’ It’s about ensuring they actually get opened. It’s achieving that balance of technical factors, best practices, and continuous monitoring. 

Ready to start landing in inboxes? Let’s dive in!

Why email deliverability matters

We’ll try to keep this simple:

• High deliverability: higher likelihood of emails landing in the inbox.
• Low deliverability: more chances of your emails landing in spam 

The real impact of low deliverability

• Lower open rates: If your emails are landing in the spam folder or being blocked by email providers, they’re not getting opened. The average open rate is 19.21%—if you see your open rates consistently decreasing, there’s something wrong.
• Fewer conversions: It follows. When emails don’t reach the inbox and they don’t get opened, then there will be no chances to convert leads.
• Missed opportunities: Each email that doesn’t make it to the inbox is a missed opportunity.
• Damaged reputation: A consistent track record of low deliverability can damage your sender reputation with email service providers (ESPs). Over time, poor deliverability can result in your emails being automatically flagged as spam, further decreasing the chances of your emails being delivered to the inbox.

The role of email providers and why you need to befriend them

Email service providers (Gmail, Outlook, and Yahoo, for example) decide whether or not your emails are worthy of reaching the inbox. They are responsible for deciding where your emails will go.

Spam filters and algorithms

ESPs use spam filters to decide whether an email is legitimate or potentially harmful. They examine factors, including the sender’s reputation, the content of the email, user feedback, and engagement metrics.

🔖 Related Reading: Spam filters: everything you need to know

Sender reputation

ESPs study bounce rates, spam complaints, and unsubscribe rates. If these metrics are low, you likely have a good sender reputation, which increases the chances of your emails being delivered.

Engagement metrics

ESPs also look at how your audience engages with your emails. They track your open rates, reply rates, and click-through rates. If the numbers show your emails are being ignored or marked as spam by recipients, ESPs will tag you as a sender with poor reputation. With poor reputation, future emails you send may be sent to the spam folder right away.

How to master the basics of email authentication

The job of authentication protocols (SPF, DKIM, and DMARC) is to verify the email you’re sending is legitimate. This lowers the risk of your domain being used for spoofing, phishing or other malicious purposes. 

🔖 Related Reading: SPF, DKIM, and DMARC: What They Are and Why You Should Care

SPF (Sender Policy Framework)

Spoofing happens when a malicious sender disguises an email and makes it appear as if it’s coming from a trustworthy source. SPF offers a method for senders to indicate the specific mail servers authorized to send emails on behalf of your domain.

🔖 Related Reading: How to Use an SPF Generator to Protect Your Domain and Improve Inboxing

DKIM (DomainKeys Identified Mail)

DKIM adds a digital signature to your emails. Here’s how it works:

• The sender’s email server uses a private key to generate this signature, which is then attached to the email’s header. 
• The recipient’s ESP uses a public key (found in your domain’s DNS records) to confirm if the signature matches.

DMARC (Domain-based Message Authentication, Reporting & Conformance)

DMARC is the next layer after SPF and DKIM. It allows senders to specify what email providers should do if certain emails fail the SPF or DKIM checks.

DMARC enables senders to request that these emails be quarantined (sent to spam) or rejected outright. It also has reporting capabilities to monitor authentication activity on your domain and understand how your emails are being treated by recipient servers.

🔖 Related Reading: Set Up DMARC in 5 Minutes with a Generator

How to master the basics of avoiding spam triggers

Seeing your emails end up in the spam folder can be frustrating. The culprit? Spam triggers. These are certain words, phrases, and elements that are flagged by spam filters as they have been known to be used by spammers consistently. 

Q: What are spam triggers?

A: Spam triggers refer to specific content, phrases, and formatting tactics that alert email filters to flag your message as potential spam. When a spam filter detects certain elements in your email, it automatically sends it to the spam folder.

🔖  Related Reading: Words That Trigger Spam Filters (And How to Fix Them with a Template Checker)

Common email content and formatting mistakes often associated with spammers or suspicious email:

• Using all capital letters for entire phrases or sentences 
• Subject lines or words like “Act Now!!!” or “Limited Time Offer!!!!” 
• Including too many links in the email body or signature
• Specific words like “free,” “guaranteed,” “risk-free,” “money-back,” and “limited time only!”
  

Best practices for crafting email content that doesn’t trigger spam filters

• Be clear and concise. Do not use jargon and salesy language. Be straightforward and to the point.
• Use relevant subject lines. Avoid clickbait phrases and focus on being specific. Instead of saying “Get FREE money today!”, try something like “Your guide to starting a profitable side business.”
• Limit your links. Keep your email content clean. One or two relevant and trustworthy links should be enough.
• Personalize the content: Use dynamic fields (ex. recipient’s name or business) to make your email feel more tailored and relevant.
  Test your emails: Use tools like Warmy’s free Template Checker to analyze your emails before sending them out. This will help you identify any hidden spam triggers and correct them before your campaign is sent.

How to master the basics of list hygiene

A clean contact list has a higher chance of emails reaching the right people. For example, if emails are sent to invalid or inactive email addresses, those emails may bounce and get returned to you. 

If this happens on a regular basis, your high bounce rates will tell email service providers (ESPs) that you do not have a legitimate or active email list. They may think you are a spammer or you might be doing something suspicious. This impacts your reputation and makes it more likely that future emails will be flagged as spam or blocked.

Here are some best practices for list hygiene:

• Regularly clean and update your email list to remove inactive subscribers. (Read more: 6 Must-Have Email List Scrubbing Tools for Spotless List Hygiene in 2025)
• Segment your list. This allows you to target the right recipients and avoid sending to irrelevant contacts. Regular segmentation improves deliverability and boosts open and click rates.

How to master the basics of warming up a new email domain

When you start using a new domain for email outreach, you can’t just suddenly send to 5,000 contacts right away. You will need to warm it up gradually to build a positive sender reputation with email service providers. 

Sending thousands of emails right away will result in your domain being flagged as suspicious, and your emails might end up in the spam folder. 

What is email warmup?

By definition, email warmup is the process of gradually increasing the volume of emails sent from a new or inactive domain. 

You send a small number of emails to carefully selected recipients and you slowly scale up the volume over time. This builds a history of trusted email activity, which will improve your domain’s sender reputation in the long run.

🔖 Related Reading: Importance of Email Warmup before Cold Outreach

Warming up the domain helps build trust with ISPs, demonstrating that the emails are legitimate and not part of a spam campaign. 

Key strategies for warming up a new domain

1. Start by sending only a small number of emails per day (no more than 20-30 emails initially). This allows ESPs to build trust in your domain without overwhelming their systems.
2. Send emails to contacts who are more likely to engage. These should be contacts who will open, read, and respond to your emails. 
3. Slowly increase the number of emails you send each day for the next few weeks. 
4. The goal is to slowly ramp up to your target sending volume while still maintaining positive engagement and minimizing bounces or complaints.
5. Keep an eye on metrics like open rates, reply rates, and click-through rates. If you notice low engagement, dial down the volume and focus on improving the content and relevance of your emails.

🔖 Related Reading: The Science and Process of Warming Up Newly Created Email Domains is a report from the Warmy Research Team that examined how different warm-up strategies affect the deliverability of emails from newly created domains.

How to master the basics of reputation management and continuous monitoring

Sender reputation plays a huge role when it comes to email deliverability. Whether your emails land in the inbox or get sent straight to the spam folder depends on how email service providers view you.

Keep these practices in mind:

1. Send high-quality content that your recipients will want to read. High engagement and positive interactions will strengthen your reputation over time.
2. Implement a double opt-in process to ensure that people on your list gave consent to receive your emails. This reduces complaints and improves engagement.
3. Don’t send emails to outdated lists. They may contain spam traps—email addresses specifically set up to catch spammers.
4. Regularly check Google Postmaster Tools. You can monitor spam reports, delivery errors, and more to ensure your emails aren’t being flagged by Gmail users.
5. Regularly check on blacklists to ensure. Being added to a blacklist can severely affect your deliverability. (Read more: Are Blacklists Killing Your Emails? A Deep Dive into How They Influence Email Providers)
6. Monitor your email authentication records. Regularly updating and reviewing these settings helps ensure that your emails are being recognized as trusted by email providers.

Master email deliverability with Warmy.io

Warmy is designed to help you master email deliverability with powerful tools that optimize your sender reputation, automate key processes, and improve your outreach results.

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