If you're sending emails to your customers, there's a good chance many of them never see your messages. They're sitting in spam folders, bouncing back, or getting silently dropped by inbox providers. In 2025, getting emails delivered is harder than ever—but it's also more important.

This guide covers everything you need to know about email deliverability: what it means, why it matters, and exactly how to fix it. No fluff, no generic advice—just the practical steps that actually work.

What Is Email Deliverability (And Why Should You Care)?

Email deliverability is the percentage of your emails that actually land in your recipients' inboxes. Not their spam folders. Not bounced. Actually delivered where people can see them.

Here's the thing most people don't realize: sending an email and delivering an email are two completely different things. Your email service provider might show "sent" for 10,000 emails, but if 30% land in spam, you've effectively lost 3,000 customers.

For SaaS companies, poor deliverability means:

Lost revenue — Trial users don't see your onboarding emails, so they never activate
Damaged reputation — Customers think you're not responsive when your emails are just getting filtered
Wasted effort — Your carefully crafted campaigns reach a fraction of your audience
Compliance issues — If transactional emails don't arrive, you might miss legal requirements

The New Rules: What Changed in 2024-2025

In February 2024, Google and Yahoo rolled out strict new requirements for bulk senders. If you send more than 5,000 emails per day to Gmail or Yahoo users, you're now considered a bulk sender and must comply with these rules:

1. Email Authentication Is Now Mandatory

Gone are the days when authentication was "nice to have." You now must have all three of these configured:

SPF (Sender Policy Framework) — Tells inbox providers which servers are allowed to send email on your behalf
DKIM (DomainKeys Identified Mail) — Adds a digital signature to prove your emails haven't been tampered with
DMARC (Domain-based Message Authentication) — Tells providers what to do with emails that fail SPF or DKIM checks

Without all three properly configured, your emails will either bounce or land in spam. There's no middle ground anymore.

2. One-Click Unsubscribe Is Required

Every marketing email must include a visible, one-click unsubscribe option. This means:

A List-Unsubscribe header in your email (handled automatically by good email providers)
An unsubscribe link that works with a single click—no login required, no confirmation pages
Processing unsubscribe requests within 2 days (ideally instant)

3. Spam Complaint Rate Limits

Google now publicly states your spam complaint rate must stay below 0.3%. Go above that, and your deliverability will suffer. The sweet spot is under 0.1%.

This means if 1,000 people receive your email and 3 of them click "Report Spam," you're at the limit. Just three people.

How Email Actually Gets Delivered (The Technical Stuff)

Understanding what happens behind the scenes helps you fix problems. Here's the simplified version:

You send an email — Your app triggers an email through your email provider
DNS lookups happen — The receiving server checks your SPF, DKIM, and DMARC records
Reputation check — The receiver looks up your sending IP and domain reputation
Content analysis — AI models scan your email for spam signals
Delivery decision — Based on all factors, the email goes to inbox, spam, or gets rejected

Each step is a potential failure point. Let's look at how to optimize each one.

Setting Up Authentication (Step by Step)

SPF Configuration

SPF tells receiving servers which IP addresses can send email from your domain. Here's how to set it up:

Go to your DNS provider (Cloudflare, Route53, etc.)
Add a TXT record for your domain
Include all services that send email on your behalf

A typical SPF record looks like this:

v=spf1 include:_spf.google.com include:sendgrid.net ~all

Common mistake: Having multiple SPF records. You can only have one, so combine all includes into a single record.

DKIM Setup

DKIM adds a cryptographic signature to your emails. Setup varies by provider, but generally:

Generate a DKIM key pair through your email provider
Add the public key as a TXT record in your DNS
Your provider automatically signs outgoing emails with the private key

The DNS record typically looks like:

selector._domainkey.yourdomain.com TXT "v=DKIM1; k=rsa; p=MIGfMA0GCS..."

DMARC Policy

DMARC ties SPF and DKIM together and tells receivers what to do with failing emails. Start with a monitoring policy:

v=DMARC1; p=none; rua=mailto:[email protected]

This sends you reports without affecting delivery. Once you're confident everything is set up correctly, move to a stricter policy:

v=DMARC1; p=reject; rua=mailto:[email protected]

Building and Protecting Your Sender Reputation

Your sender reputation is like a credit score for email. It's built over time and can be destroyed quickly. Here's what affects it:

Factors That Help Your Reputation

High open rates — People engaging with your emails signals they're wanted
Low bounce rates — A clean list shows you're collecting emails properly
Consistent sending volume — Steady patterns look legitimate
Low spam complaints — The most important factor
Email replies — Recipients replying is a strong positive signal

Factors That Hurt Your Reputation

Spam traps — Hitting email addresses specifically set up to catch spammers
High hard bounce rates — Sending to invalid addresses suggests a purchased or scraped list
Sudden volume spikes — Going from 100 emails/day to 100,000 looks suspicious
Spam complaints — Even a few can tank your reputation
Blacklist appearances — Getting listed on DNS blocklists

Warming Up a New Domain or IP

If you're starting fresh with a new domain or IP address, you need to warm it up. Inbox providers are suspicious of new senders—for good reason, since most spammers use fresh domains.

Here's a realistic warmup schedule:

Week	Daily Volume	Focus
1	50-100	Only your most engaged users
2	200-500	Expand to recent openers
3	1,000-2,000	Include active subscribers
4	5,000-10,000	Most of your list
5+	Full volume	Everyone

Key principle: Send to people most likely to engage first. Their opens and clicks build your reputation for the larger sends later.

Content That Doesn't Trigger Spam Filters

Modern spam filters use machine learning to analyze email content. While there's no magic formula, certain patterns help:

Things to Avoid

ALL CAPS in subject lines or body text
Excessive punctuation (!!!!! or $$$$$)
Spammy phrases like "Act now!" "Limited time!" "Free money!"
Image-only emails with no text
Shortened URLs (bit.ly, etc.) — they're commonly used by spammers
Mismatched "From" names and domains
Attachments in marketing emails

Things That Help

Personalization (using the recipient's name naturally)
Plain text versions alongside HTML
Consistent sender information
Proper HTML structure
A healthy text-to-image ratio
Links to your primary domain (not random tracking domains)

List Hygiene: The Unsexy But Essential Part

Your email list degrades over time. People change jobs, abandon email addresses, or simply lose interest. Regular cleaning is essential:

Remove These Addresses

Hard bounces — Remove immediately and never send again
Soft bounces — After 3-5 consecutive soft bounces, remove them
Long-term inactive — No opens in 6+ months? Consider a re-engagement campaign, then remove non-responders
Role addresses — support@, info@, admin@ rarely help your metrics

Validate Before Sending

Use email validation services to check addresses before adding them to your list. They can identify:

Invalid syntax
Non-existent mailboxes
Known spam traps
Disposable email addresses
Role-based addresses

Monitoring Your Deliverability

You can't fix what you don't measure. Here's what to track:

Key Metrics

Delivery rate — Percentage of emails accepted by receiving servers
Inbox placement rate — Percentage that actually land in inbox (not spam)
Open rate — Can indicate deliverability problems if suddenly dropping
Bounce rate — Keep under 2%
Spam complaint rate — Keep under 0.1%

Tools for Monitoring

Google Postmaster Tools — Free, essential for Gmail deliverability data
DMARC reports — Your DMARC policy generates reports showing authentication results
Blacklist monitors — Check if your IP/domain appears on blocklists
Seed list testing — Send to test addresses across providers to see where you land

When Things Go Wrong: Troubleshooting

Sudden Drop in Deliverability

If your metrics suddenly tank:

Check your authentication records — did something change?
Look for blacklist appearances
Review recent list changes — did you add unverified addresses?
Check for complaints about recent campaigns
Verify your sending infrastructure hasn't changed

Gmail-Specific Issues

Gmail is the hardest to crack. If you're having Gmail problems:

Set up Google Postmaster Tools immediately
Check your domain reputation in Postmaster
Look for authentication failures
Review your spam rate trend
Send a re-engagement campaign to your most active Gmail users first

The Bottom Line

Email deliverability isn't magic—it's a set of technical requirements and best practices that, when followed consistently, get your emails where they need to go.

The most important things to remember:

Set up authentication properly — SPF, DKIM, and DMARC are non-negotiable
Protect your reputation — Send to engaged users, keep complaints low
Keep your list clean — Remove bounces, validate new addresses
Monitor constantly — Problems are easier to fix when caught early
Send content people actually want — The best deliverability strategy is sending emails people are happy to receive

If you're building a SaaS product and want deliverability handled for you, that's exactly what we built Sequenzy to do. We take care of authentication, warming, reputation management, and monitoring so you can focus on your actual business.