Email Deliverability Guide: Why Emails Go to Spam (And How Forward Helps)

You've crafted the perfect email. You hit send. And then... nothing. No reply. No open. Your message is sitting in a spam folder somewhere, unread and ignored.

It's frustrating, but it's also common. Up to 20% of legitimate emails never reach the inbox — they're blocked or filtered as spam. If you're running a business, that's lost opportunities, missed connections, and potentially damaged reputation.

In this guide, we'll break down exactly why emails go to spam, how to diagnose your deliverability issues, and most importantly, how to fix them. We'll also show how Forward's built-in authentication tools can help.

Why Emails Go to Spam: The Root Causes

Email providers like Gmail, Outlook, and Yahoo use complex algorithms to decide whether your email lands in the inbox or gets buried in spam. These systems evaluate three main factors:

Let's dive into each one.

1. DNS Authentication Issues

This is the #1 reason legitimate emails go to spam. If your domain lacks proper DNS authentication, email providers can't verify that you are who you say you are.

The Big Three: SPF, DKIM, and DMARC

Think of these as your email's passport, signature, and enforcement policy:

SPF (Sender Policy Framework)

What it does: SPF is a DNS record that lists which mail servers are authorized to send email on behalf of your domain. It's like a guest list at an exclusive club — if you're not on the list, you don't get in.

Example SPF record:

v=spf1 include:_spf.google.com include:forward.mx ~all

This says: "Allow Google's mail servers and Forward's servers to send email from my domain. Everything else should be flagged."

DKIM (DomainKeys Identified Mail)

What it does: DKIM adds a cryptographic signature to your emails. When a receiving server gets your email, it checks the signature against a public key in your DNS records. If they match, the email hasn't been tampered with.

Why it matters: DKIM proves that the email actually came from your domain and wasn't modified in transit. Without it, anyone could spoof your email address.

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

What it does: DMARC ties SPF and DKIM together and tells receiving servers what to do if an email fails authentication checks.

Example DMARC record:

v=DMARC1; p=quarantine; rua=mailto:dmarc@yourdomain.com

This says: "If an email fails SPF or DKIM checks, quarantine it (send to spam). Send daily reports to dmarc@yourdomain.com so I can monitor what's happening."

How Forward Handles Authentication

If you're using Forward for email forwarding, you get built-in support for all three protocols:

• SPF: Forward provides the correct include:forward.mx syntax to add to your existing SPF record
• DKIM: Forward automatically signs forwarded emails with DKIM, preserving authentication through the forwarding chain
• DMARC: Forward is compatible with your DMARC policy and provides guidance on proper setup

Learn more about Forward's authentication features →

2. Sender Reputation Problems

Your sender reputation is like a credit score for email. It's built over time based on your sending behavior. A good reputation means your emails get delivered. A bad reputation means they don't.

What Hurts Your Reputation

• High bounce rate: Sending to invalid or non-existent addresses
• Spam complaints: Recipients marking your emails as spam
• Low engagement: Emails that are rarely opened or clicked
• Inconsistent sending patterns: Burst sending (lots of emails suddenly, then nothing for weeks)
• Being on blacklists: Your domain or IP listed on spam databases
• New domain: Domains less than 6 months old have "cold" reputations

How to Check Your Reputation

Use these free tools to audit your sender reputation:

• Google Postmaster Tools: Free dashboard showing your domain's reputation with Gmail (accounts for ~40% of all email)
• MXToolbox: Check if your domain is on blacklists
• Mail Tester: Send a test email and get a detailed score with specific recommendations
• DMARC reports: If you have DMARC set up, review the daily reports to see authentication failures

Building a Good Reputation

1. Warm up new domains slowly: Start with 10-20 emails/day and gradually increase over 2-4 weeks
2. Only email people who opted in: Never buy email lists
3. Clean your list regularly: Remove bounces and unengaged subscribers every 3-6 months
4. Make unsubscribing easy: One-click unsubscribe reduces spam complaints
5. Send consistently: Regular sending (even if low volume) is better than sporadic bursts

3. Email Content Issues

Even with perfect authentication and a spotless reputation, your emails can still hit spam because of what you're sending.

Spam Trigger Words

Certain words and phrases in your subject line or body can trigger spam filters. Some classic examples:

• FREE, FREE FREE (especially in all caps)
• Act now, Limited time, Urgent
• $$$ or excessive dollar signs
• Click here, Click below
• Winner, Congratulations, You've been selected
• 100% free, No obligation, Risk-free
• Dear friend, Dear customer (generic greetings)

Other Content Red Flags

• ALL CAPS: Feels like shouting, triggers filters
• Excessive punctuation!!! Especially in subject lines
• Broken links: Links that don't work or go to suspicious sites
• Image-heavy emails: Emails that are mostly images with little text
• Attachments: Unexpected attachments (especially .exe, .zip) trigger warnings
• Shortened URLs: Bit.ly, TinyURL, etc. can look suspicious
• Mismatched links: Link text says "Google" but URL goes elsewhere

Content Best Practices

• Balance text and images: Aim for at least 60% text, 40% images
• Include a text version: Always provide a plain-text alternative to your HTML email
• Use descriptive subject lines: Clear, honest, and specific
• Personalize when possible: Use the recipient's name
• Include physical address: Required by law (CAN-SPAM) and builds trust
• Clear unsubscribe link: Make it obvious and one-click

Step-by-Step Troubleshooting Guide

If your emails are going to spam, follow this diagnostic process to identify and fix the issue:

Step 1: Check Your DNS Records

1Verify your SPF, DKIM, and DMARC records exist and are correct.

Use these commands in your terminal or an online DNS checker:

• SPF: dig TXT yourdomain.com (look for v=spf1)
• DKIM: dig TXT selector._domainkey.yourdomain.com
• DMARC: dig TXT _dmarc.yourdomain.com

If any of these are missing, that's your problem. Set them up immediately.

Step 2: Test Your Email Score

2Send a test email to Mail Tester (mail-tester.com).

1. Go to mail-tester.com
2. Copy the test email address they provide
3. Send your email to that address
4. Check your score (aim for 8+/10)
5. Review the detailed breakdown for specific issues

This will tell you exactly what's wrong: missing authentication, spammy content, broken links, blacklisted IPs, etc.

Step 3: Check Blacklists

3Verify your domain and sending IP aren't blacklisted.

Use MXToolbox Blacklist Check:

1. Go to mxtoolbox.com/blacklists.aspx
2. Enter your domain name
3. Review results — any red listings need to be addressed

If you're blacklisted, you'll need to request delisting from each blacklist. This can take anywhere from 24 hours to 2 weeks.

Step 4: Review Google Postmaster Tools

4If you send to Gmail addresses, check your domain reputation.

1. Go to postmaster.google.com
2. Add and verify your domain
3. Wait 24-48 hours for data to populate
4. Check domain reputation, spam complaint rate, and delivery errors

A "Low" or "Bad" reputation in Postmaster Tools explains why Gmail is filtering your emails.

Step 5: Analyze DMARC Reports

5If you have DMARC set up, review the aggregate reports.

DMARC reports show you exactly which emails are passing or failing authentication. Look for:

• Sources sending email on your behalf that aren't in your SPF record
• Failed DKIM signatures (could indicate tampering or misconfiguration)
• Unknown IP addresses sending from your domain (potential spoofing)

Tools like DMARC Analyzer or Dmarcian can parse these XML reports into readable dashboards.

Step 6: Test with Real Email Providers

6Send test emails to Gmail, Outlook, Yahoo, and other providers.

Create test accounts on each major provider and send emails to yourself. Check if they land in inbox or spam. This gives you real-world feedback across different filtering systems.

Email Deliverability Best Practices

Once you've fixed immediate issues, follow these practices to maintain good deliverability long-term:

Technical Setup

• Set up all three authentication protocols: SPF, DKIM, and DMARC are non-negotiable
• Use a custom domain: Don't send business email from @gmail.com
• Monitor DMARC reports: Check weekly for authentication failures
• Keep SPF updated: When you add new sending services, update your SPF record
• Consider a dedicated IP: For high volume (100K+ emails/month), a dedicated IP gives you full control over reputation

List Management

• Double opt-in: Require email confirmation before adding to list
• Regular list cleaning: Remove bounces, complaints, and unengaged subscribers
• Segment your list: Send relevant content to relevant people
• Never buy email lists: This will destroy your reputation
• Honor unsubscribes immediately: Required by law and good practice

Sending Behavior

• Warm up new domains: 2-4 weeks of gradually increasing volume
• Send consistently: Regular cadence (daily, weekly, monthly)
• Don't blast inactive subscribers: If they haven't opened in 6 months, re-engage or remove
• Monitor engagement metrics: Open rate, click rate, spam complaints
• Respond to spam complaints: Remove complainants and figure out why it happened

Email Content

• Clear, honest subject lines: No clickbait or deception
• Text-to-image balance: 60%+ text
• Mobile-friendly design: 60%+ of emails are opened on mobile
• Plain text alternative: Always include for accessibility
• Personalization: Use recipient's name when available
• Physical mailing address: Required by CAN-SPAM Act
• Easy unsubscribe: One-click, visible, and works

How Forward Improves Your Deliverability

Forward is built with email deliverability in mind. When you use Forward for email forwarding, you get:

Built-in Authentication Support

• SPF-compatible: Forward provides the correct SPF record syntax to include in your domain's configuration
• DKIM signing: Forwarded emails are automatically signed with DKIM, preserving authentication through the forwarding process
• DMARC alignment: Forward works correctly with your DMARC policy, ensuring authenticated emails stay authenticated

Clean Infrastructure

• Reputable IP addresses: Forward's sending infrastructure maintains good reputation with major email providers
• Not on blacklists: Forward monitors and maintains clean IP reputation
• Proper reverse DNS: All Forward IPs have correct PTR records

Easy Setup

Instead of managing complex email infrastructure yourself, Forward gives you:

• Simple DNS configuration with clear instructions
• Automatic DKIM key management
• Clear documentation for SPF and DMARC setup
• Support for troubleshooting deliverability issues

Explore all Forward features →

Common Scenarios and Solutions

Scenario 1: New Domain, Everything Goes to Spam

Diagnosis: Cold domain reputation + possibly missing authentication

Solution:

1. Set up SPF, DKIM, DMARC immediately
2. Start with p=none DMARC policy to monitor
3. Warm up slowly: 10-20 emails/day, increasing over 4 weeks
4. Focus on engaged recipients first (people who opted in)
5. Monitor Google Postmaster Tools for reputation changes

Scenario 2: Used to Work, Now Goes to Spam

Diagnosis: Reputation drop, blacklist, or configuration change

Solution:

1. Check blacklists (MXToolbox)
2. Review Google Postmaster Tools for spam complaints
3. Check DMARC reports for authentication failures
4. Verify SPF/DKIM/DMARC are still configured correctly
5. Look for recent sending behavior changes (volume spikes, new content)

Scenario 3: Gmail Works, Outlook Doesn't

Diagnosis: Different filtering algorithms, possibly IP reputation

Solution:

1. Check Outlook Smart Network Data Services (SNDS)
2. Verify IP isn't on Outlook-specific blacklists
3. Review email content for Outlook-specific triggers
4. Ensure proper formatting (Outlook is pickier about HTML)

Scenario 4: Transactional Emails Go to Spam

Diagnosis: Usually missing authentication or shared IP with bad reputation

Solution:

1. Set up SPF, DKIM, DMARC for your sending domain
2. If using a shared sending service, consider dedicated IP
3. Include clear branding in transactional emails
4. Don't mix marketing content with transactional emails

FAQ

How long does it take to fix email deliverability?

It depends on the issue. DNS changes propagate in minutes to hours. Blacklist removal can take 24 hours to 2 weeks. Reputation recovery takes weeks to months of good sending behavior.

Can I recover from a bad sender reputation?

Yes, but it takes time. Stop sending to unengaged subscribers, clean your list, and send consistently good content for 2-3 months. Reputation gradually improves with positive signals.

Is a dedicated IP worth it?

For most senders under 50,000 emails/month: no. Shared IPs from reputable providers (like Forward) are fine. Consider dedicated IP when you're sending 100K+ emails/month and have the expertise to manage IP reputation.

Do email forwarding services hurt deliverability?

Not if set up correctly. Forward preserves authentication through proper DKIM signing and ARC (Authenticated Received Chain) headers. The key is including Forward in your SPF record and using a DMARC-compatible setup.

What's a good spam complaint rate?

Under 0.1% (1 complaint per 1,000 emails) is good. Under 0.01% is excellent. Above 0.1% will start hurting your reputation. If you're above 0.5%, you have a serious problem.

Final Checklist

Before you consider your email deliverability "done," make sure you've completed:

• ✅ SPF record configured and tested
• ✅ DKIM signature working
• ✅ DMARC policy set (start with p=none, move to p=quarantine)
• ✅ Google Postmaster Tools set up
• ✅ Not on any blacklists
• ✅ Mail Tester score of 8+/10
• ✅ Test emails reach inbox at Gmail, Outlook, Yahoo
• ✅ List cleaned (no bounces, complaints handled)
• ✅ Clear unsubscribe link in every email
• ✅ Consistent sending schedule established

Email deliverability isn't a one-time fix — it's an ongoing practice. Monitor your metrics, respond to issues quickly, and always prioritize sending email people actually want to receive.