Email Deliverability for SaaS: A Practical Guide

TL;DR

Email deliverability determines whether your messages reach inboxes or spam folders. The fundamentals: set up DNS authentication (SPF, DKIM, DMARC), use reputable email providers with good IP reputation, only email people who opted in, make unsubscribe easy, and remove bounced/ inactive addresses promptly. Key insight: marketing emails can hurt transactional deliverability if sent from same infrastructure - consider separation at scale. Most deliverability issues stem from: purchased lists, missing authentication, high bounce rates, or sudden volume spikes. Platforms like Sequenzy ($19/mo with free trial) handle authentication setup, bounce processing, and sender reputation management automatically.

The Basics: DNS Authentication

Three DNS records matter. Set them up correctly once and mostly forget about them.

SPF (Sender Policy Framework)

SPF tells receiving servers which mail servers are allowed to send email for your domain. It's a TXT record that lists authorized senders.

Your email provider will give you the specific value. It looks something like:

v=spf1 include:_spf.provider.com ~all

Common mistake: Having multiple SPF records. You can only have one. If you use multiple email services, combine them into one record.

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to your emails. The receiving server can verify the email wasn't tampered with and actually came from you.

Your email provider generates DKIM keys. You add their public key as a DNS record. They sign outgoing emails with the private key.

Setup: Follow your provider's instructions. It's usually adding a CNAME or TXT record with a specific selector name.

DMARC (Domain-based Message Authentication)

DMARC tells receiving servers what to do when SPF or DKIM fail. It also enables reporting so you can see who's sending email as your domain.

Start with a monitoring-only policy:

v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com

After monitoring for a few weeks and confirming everything's working, move to enforcement:

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

Or strict rejection:

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

Sender Reputation

Email providers (Gmail, Outlook, etc.) track your sending reputation. Good reputation = inbox. Bad reputation = spam folder.

What builds good reputation:

• People open your emails. High open rates signal wanted mail.
• People click links. Engagement indicates value.
• People reply. Strongest signal of legitimacy.
• Low bounce rates. You're sending to valid addresses.
• Few spam complaints. People aren't marking you as junk.

What damages reputation:

• High bounce rates. Sending to invalid addresses looks spammy.
• Spam complaints. Even 0.1% complaint rate is concerning.
• Spam traps. Old addresses turned into honeypots.
• Sudden volume spikes. Going from 100 to 10,000 emails overnight looks suspicious.
• Inconsistent sending. Sporadic large bursts then silence.

Practical Guidelines

For transactional email

Transactional emails (password resets, receipts) have naturally high engagement. People expect and open them. Your main risks:

• Sending to bad addresses. Implement email verification at signup.
• Slow delivery. Use a provider known for speed (Postmark, Resend).
• Getting mixed with marketing. Consider separate infrastructure if you send high marketing volume.

For marketing email

Marketing emails face more scrutiny. Guidelines:

• Only email people who opted in. Never buy lists. Never scrape addresses.
• Make unsubscribe easy. One click. No login required.
• Clean your list regularly. Remove bounced addresses immediately. Remove chronically unengaged subscribers periodically.
• Warm up new sending domains. Start with small volumes to engaged subscribers, gradually increase.
• Send consistently. Regular sending patterns build reputation better than sporadic blasts.

What Your Email Provider Handles

Good email providers (Sequenzy, Resend, Postmark, Customer.io) handle:

• IP reputation management
• Bounce processing
• Feedback loop processing (spam complaints)
• List-Unsubscribe headers
• Automatic suppression of problem addresses

You don't need to manage these yourself. Pick a reputable provider and let them handle the infrastructure.

Testing Deliverability

Before major campaigns:

1. Send test emails to your own Gmail, Outlook, Yahoo accounts
2. Check if they hit inbox or spam
3. Use tools like Mail-Tester.com for detailed analysis
4. Check your domain reputation at Google Postmaster Tools (if you send significant volume to Gmail)

Red Flags to Watch

• Open rates dropping suddenly. Might be deliverability, might be content. Investigate.
• Bounce rates above 2%. Something's wrong with your list hygiene.
• Spam complaints above 0.1%. Review your sending practices.
• Emails going to spam for specific providers. Check authentication and content for that provider's guidelines.

What Doesn't Matter Much

Things people worry about that rarely cause actual problems:

• Email length. Gmail doesn't penalize long emails.
• Images vs text ratio. Old spam filter logic, mostly irrelevant now.
• Certain "spam trigger words." "Free" in your subject line won't tank deliverability.
• Sending time optimization. Matters more for opens than delivery.

The Bottom Line

1. Set up SPF, DKIM, and DMARC correctly
2. Use a reputable email provider
3. Only email people who want to hear from you
4. Make unsubscribe easy
5. Remove bad addresses promptly

That's 90% of deliverability. The remaining 10% is edge cases you'll handle as they come up.

Deliverability Platform Comparison

Platform	Deliverability Focus	Authentication Help	IP Management
Postmark	Transactional specialist	✓ Excellent guides	Dedicated IPs
Resend	Developer-focused	✓ Good docs	Shared/Dedicated
Sequenzy	SaaS marketing	✓ Setup assistance	Managed pools
Mailchimp	Small business	✓ Basic	Shared pools
AWS SES	Technical users	✗ DIY required	Self-managed

How Email Deliverability Works

Email deliverability is determined by multiple factors:

1. Authentication: SPF, DKIM, DMARC verify you're authorized to send from your domain
2. Sender Reputation: IP and domain reputation scores based on historical sending behavior
3. Content Quality: Spam filters analyze content patterns (less important than reputation)
4. Engagement Signals: Open rates, reply rates, spam complaints affect future delivery
5. Infrastructure: IP warming, dedicated vs shared IPs, geographical sending location
6. List Hygiene: Bounce rates, spam trap hits, complaint rates impact sender score

Receiving providers (Gmail, Outlook, etc.) combine these signals to decide placement: inbox, spam, or rejection. Good reputation means consistent inbox placement. Poor reputation means spam folder or blocking.

Best Practices

Authentication Setup

• Set up SPF, DKIM, and DMARC for all sending domains
• Use DMARC reporting to monitor authentication failures
• Start with p=none, move to p=quarantine, then p=reject
• Authenticate all subdomains used for sending
• Test authentication using tools like Mail-Tester.com

Sender Reputation Management

• Warm up new sending domains gradually (start small, increase volume)
• Maintain consistent sending patterns (no sudden spikes)
• Keep bounce rates below 2% and spam complaints below 0.1%
• Remove bounced addresses immediately after first hard bounce
• Re-engage or remove inactive subscribers quarterly

List Hygiene

• Use double opt-in to confirm email addresses
• Implement email verification at signup for transactional
• Never purchase or scrape email lists
• Honor unsubscribe requests immediately (within 10 days legally, instantly preferred)
• Regularly clean inactive subscribers (no engagement 6+ months)

Frequently Asked Questions

Why are my emails going to spam?

Most common causes: missing SPF/DKIM/DMARC authentication (easiest fix), sending to purchased or scraped lists (very damaging), high bounce rates from poor list quality, sudden volume increases (looks spammy), spam complaints from recipients, or shared IP reputation issues if using low-cost provider. Fix by: setting up authentication, cleaning your list, warming up gradually, switching to reputable provider, and only emailing opt-in subscribers.

How do I set up SPF, DKIM, and DMARC?

SPF: Add TXT record at your domain specifying authorized senders. DKIM: Add CNAME or TXT record with public key from your email provider. DMARC: Add TXT record with policy (start with p=none for monitoring). Your email provider provides specific values. Use tools like MXToolbox to verify records are published correctly. Most modern email platforms guide you through setup with copy-paste DNS records.

Should I use a dedicated IP for email sending?

Dedicated IPs make sense when: sending 100k+ emails monthly, you have strict deliverability requirements, or you're hitting reputation issues on shared IPs. For most businesses under 100k monthly emails: shared IPs with reputable providers (Postmark, Sequenzy, Resend) work fine and are more cost-effective. Dedicated IPs require warming from scratch and your reputation depends entirely on your practices. Shared IPs benefit from provider's overall reputation management.

What's IP warming and why does it matter?

IP warming is gradually increasing sending volume from a new IP or domain to build reputation. Send 50 emails day 1, 100 day 2, 200 day 3, gradually increasing over 2-4 weeks. This establishes positive sending patterns. Skipping warming and sending high volume immediately triggers spam filters. Most providers handle warming automatically for shared IPs. For dedicated IPs, you'll manage warming yourself or work with provider's warmup program.

How do I check my email deliverability?

Test methods: Send test emails to Gmail, Outlook, Yahoo accounts and check placement (inbox vs spam), use Mail-Tester.com for detailed analysis, check Google Postmaster Tools (if sending significant volume to Gmail), monitor bounce and complaint rates in your email platform, and track open rates (sudden drops may indicate deliverability issues). For enterprise senders, consider deliverability monitoring tools like GlockApps or MailGenius.