Email Deliverability Demystified: A Simple Guide for Startups & Solo Founders

Whether sending cold emails to generate leads, newsletters to engage your audience, or outreach to potential investors—email deliverability is critical to making sure you get noticed and actually get the engagement you need.

After all, email has an ROI of $36 per $1 spent—it’s no wonder solo founders and startup CEOs want in on that action. But if your emails are consistently ending up in the spam folder or promotions folder, and never landing in the intended recipients’ inbox, it will all be in vain.

And the fact is, email deliverability is one of those under-the-hood parts of your outreach strategy that can mean the difference between the success or failure of your efforts. For startups and solo founders who wear multiple hats, email deliverability issues can fly under the radar until it’s too late.

What is email deliverability and why does it matter?

Email deliverability refers to whether or not the emails you send end up in your recipient’s inbox, or if it is blocked, or sent to spam (or any other prebuilt folder such as promotions).

🔖 Read more: Email Deliverability: Complete Guide for 2025

It’s a vital measurement for any email marketing or outbound outreach campaign. If your emails aren’t landing in a recipient’s inbox, they can’t do the job you need them to do. In other words:

• High deliverability = more opportunities of emails making it to the inboxes 
• Low deliverability = more of your emails are likely to hit the spam folders

The way forward is clear—high deliverability is key to email outreach success. You might think it’s pretty straightforward, right? Well, email deliverability is a multi-faceted beast. There are multiple factors that contribute to that, and we’ll discuss them below.

Typical deliverability issues startups face

For startups, especially those in the early stages, email deliverability can be a particularly tough nut to crack. Here are some of the challenges that a lot of new businesses battle with when it comes to email outreach:

• New domain: A lot of startups email from a new domain. Email Service Providers (ESPs), including Gmail and Yahoo, are often suspicious of new domains. So, if you have no sending history yet, then you also don’t have a reputation. If other things or elements are red flags, your message might be tagged as spam and not get delivered to the inbox.
• Limited reputation: If your domain or IP address does not have a track record of sending legitimate, high-quality emails, you are more likely to be filtered or blocked. It takes a bit of time to build up a strong sender reputation, but it’s important for achieving high deliverability.
• Not knowing the tech: A lot of solo founders and small team startups don’t have the technical skills to set up things like DNS records (SPF, DKIM, and DMARC), and you need this to prove you are who you say you are when it comes to sending that email.  When you lack the proper verification, your emails are also more prone to end up in spam.

Key components of email deliverability

Reaching high email deliverability is a matter of identifying and taking care of key factors which help decide what happens to your emails when they’re on their way to the inbox, or how they end up being blocked. 

Email authentication: how to verify your credibility

That means you’ll be setting up some records, such as SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting & Conformance).

They all work together to protect against spoofing and phishing attacks, while ensuring emails sent on your behalf are viewed as legitimate by email providers.

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

Sender reputation: how ESPs see you

Your sender reputation is pretty much the track record of your email domain. It’s something you build up over time by how the recipients interact with your emails, such as open rates, click-through rates and complaints.

• A higher sender reputation will help ensure more of your emails being delivered to inboxes
• A bad reputation may lead to your emails being blocked, or delivered to spam.

Spam triggers and spam filters: how to evade them

• Spam triggers are words, phrases, or practices that email service providers believe are evidence that you’re spam. These include things like over salesy language, too many links, or sketchy attachments.
• Spam filters are the algorithms that screen incoming email for spam behaviors, and decide whether to let that email go through to the inbox.

Knowing spam triggers and how to avoid them will allow your emails to steer clear of your prospects’ spam folders.

Warmup process: the underrated hero of deliverability

Warming up new domains is the process of sending a small volume of emails from a new domain and increasing that gradually to establish trust with the major ESPs.

When you start to email thousands of emails from a brand new domain right off the bat, you’re going to alert the spam filters. Warming your domain is one of the best things you can do to ensure your emails have a solid sender reputation over time—and that is huge when it comes to the success of outreach campaigns.

🔖 Relevant Reading: Importance of Email Warmup before Cold Outreach

How to properly set up email authentication protocols

Did you know that around 3.4 billion emails a day are sent by cybercriminals and these are designed to appear that they are from trusted senders? Gmail also blocks roughly 100 million phishing emails daily. 

When it comes to building a strong relationship with ESPs, authentication is everything and it’s essential to deliverability success. With SPF, DKIM, and DMARC properly configured, your emails won’t get junked, and your sender reputation will also benefit.

• SPF (Sender Policy Framework): SPF verifies whether the email is really coming from the people in the email, and not from nefarious hackers. To set this up, you need to add an SPF record to your domain’s DNS, which then serves as a “whitelist” for your mail servers. (Read more: How to Use an SPF Generator to Protect Your Domain and Improve Inboxing)
• DKIM (DomainKeys Identified Mail): This is a digital signature that enables the recipient’s server to verify that the mail came from you and wasn’t altered in transit.
• DMARC (Domain-based Message Authentication, Reporting, and Conformance): DMARC links SPF and DKIM to a policy that tells email servers what to do with emails that don’t meet the requirements of those authentication methods. It also provides reports about your domain’s email activity, so you can track and enforce your email authentication policies. (Read more: Don’t Let Your Emails Get Spoofed: How a DMARC Generator Helps)

How to build a healthy sender reputation

Think of sender reputation as essentially your “email credit score.” It reflects your domain’s email sending behavior and helps determine whether your emails are allowed to land in the inbox or should be rerouted to spam instead. 

What is a sender reputation?

• It is a number that ESPs give to your domain or IP address, based on several factors (engagement, bounces, complaints).
• ESPs use this reputation score to figure out if your emails can be trusted.
• Having a good reputation as a sender is what allows your emails to get to the inbox and having a bad reputation is what can result in your emails being rejected or falling into spam boxes.

Key factors that affect your sender reputation

• Engagement: When recipients open, read, and engage with your emails, this sends a message to ESPs that you are trustworthy and that you send relevant content. 
• Complaint rates: People will let you know you are doing something wrong by filling out a spam report. Lower rates of complaints are necessary for a favorable reputation. (Read more: Spam Complaint Rate: What It Is and How to Reduce It)
• Bounce rates: Emails that fail to be delivered because of invalid addresses or server issues contribute to a high bounce rate. High bounce rates are also a sign to ESPs that you may have a poor quality email list. (Read more: Bounced Emails: Understanding Causes and Solutions for Gmail, Outlook, and Yahoo)

How to maintain a positive sender reputation

Keep up a good sender reputation and cultivate best practices when it comes to email-sending behavior. Here’s some practical advice for how to build and maintain a good name:

• Grow your reputation slowly. Take it slow and build up to an ideal sending volume to establish a strong reputation.
• Clean your list frequently: Remove all invalid or non-engaged contacts from your list so that your bounce rates can remain low. Using unverified lists can damage your reputation quickly.
• Watch your email metrics: Keep an eye on open rates, bounce rates and complaint rates on an ongoing basis. If you see a negative trend, tackle it right away. Tracking those can enable you to clear troubles in a timely manner before they do long lasting injury to your reputation.
• Use double opt-in: A double opt-in process for your email list ensures that subscribers genuinely want to receive your emails. This is a strategy to lower spam complaints and to raise engagement.
• Steer clear of spam triggers: Watch your use of spammy words, overuse of punctuation marks, and suspicious looking attachments in your emails. Emails should be professional, timely and personalized.

How startups can successfully evade spam filters

The single biggest problem affecting email deliverability is getting your emails in the inbox. This can be particularly difficult for startups, when new domains or new email addresses are more often filtered by ESPs.

Common spam triggers and how to avoid them

Spam filters are complex and look at things like body content, email sender behavior, and other factors to tell if an email is safe or spam. These filters are meant to shield people from unwanted emails—but sometimes they are too aggressive, and can flag even legitimate outreach as spam.

There are some of the most common spam triggers to keep in mind:

• Deceptive subject lines:  If the subject lines mislead or over sell before someone even opens the email, that’s an obvious red flag! Examples: “Free,” “Limited Offer,” or “Urgent Action Required”
• Overuse of sales language, words, or phrases: Some words and phrases are notorious for being spam. Think “Buy now,” “Limited time,” “Act fast,” or “Risk-free.”
• Too many links: Emails with lots of links, particularly links to unverified or spammy sites, can most likely cause spam filters to go off. 
• Large attachments or sketchy files: Attachments are a common way for spammers to deliver malware.
• Overuse of images: Emails containing more images than text might be distrustful in the eyes of the spam filters, since spammers tend to use images to conceal spammy material and keywords.
• No legal mandates and option to unsubscribe: Spam laws like the CAN-SPAM Act also require that there be an easy way for recipients to remove themselves from a list so that they stop receiving emails from that particular sender in the future.

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

How to implement proper warmup

Email warm-up is a critical step in building a solid sender reputation and ensuring that your emails land in the inbox. It’s the concept of slowly turning the volume up on your emails from a new domain or mailbox.

When you are new to sending email from a new domain or email address, ESPs are on guard to identify whether you are a legitimate sender or spammer. In order to gain trust and not to be flagged as spam, its all about warming up your domain or mailbox gradually over time.

How to use Warmy for email warmup