Mailbase
Start free
DeliverabilityUpdated · 7 min read

Email Deliverability Basics for SaaS Founders

Email deliverability explained for founders: the five things that decide whether you reach the inbox — authentication, reputation, list hygiene, engagement, and compliance — and how to monitor them.

MT
Mailbase Team
email deliverability basics
On this page · 8 sections

Overview

Email deliverability is whether your email actually reaches the inbox — not just whether it's "sent." A message can be accepted by the provider and still land in spam or get silently dropped, so "delivered" and "in the inbox" are different things. For a SaaS founder it matters everywhere: password resets, receipts, onboarding, and campaigns are all worthless if they don't arrive. The good news is that deliverability isn't luck or a magic provider setting — it's five controllable pillars.

The five pillars of deliverability

1. Authentication — prove you are who you say with SPF, DKIM, and DMARC; Gmail and Yahoo now effectively require it for bulk senders. 2. Sender reputation — your domain and IP build a track record providers score; it's earned slowly and lost fast. 3. List hygiene — only send to verified, engaged addresses, because bounces and spam traps wreck reputation.

4. Engagement — opens, replies, and "not spam" raise placement; deletes and complaints sink it, so relevance is a deliverability tactic, not just a marketing one. 5. Compliance — honor unsubscribes, include a physical address, and respect consent laws. Get these five right and good content does its job; get them wrong and the best email sits in spam.

  • Authentication: SPF, DKIM, DMARC passing
  • Reputation: domain/IP track record — slow to build, fast to lose
  • List hygiene: verified, engaged addresses only
  • Engagement: relevance drives inbox placement
  • Compliance: unsubscribe, address, consent

What to monitor (and the numbers to watch)

You can't manage what you don't measure. Watch bounce rate (keep under ~2%), spam-complaint rate (under ~0.3% — Google's threshold), and engagement trends by segment. Set up Google Postmaster Tools and your provider's analytics so a reputation dip shows up before it becomes a crisis, and separate transactional from marketing sending so a bad campaign can't take down your password resets. Start by checking your authentication with the free domain check.

If mail is already landing in spam, work the pillars in order — fix authentication first, then list hygiene, then content — rather than tweaking subject lines. The full checklist is in how to avoid the spam folder.

  • Bounce rate under ~2%; complaint rate under ~0.3%
  • Use Google Postmaster Tools + provider analytics
  • Separate transactional and marketing streams
  • Debug in order: auth → hygiene → content

Common mistakes

  • Skipping SPF, DKIM, and DMARC, or assuming they're a one-time setup.
  • Sending real volume from a brand-new, un-warmed domain.
  • Reusing a stale list without re-verifying, so bounces spike.
  • Ignoring complaint rate until a single bad campaign sinks the domain.

Sources and further reading

Official docs for current setup details, pricing, and API behavior — verify specifics there, since they change.

Amazon SES docsSupabase custom SMTP docs

Related guides

More on email deliverability basics and the surrounding deliverability workflow:

free domain checkSPF, DKIM, and DMARCdeliverability and honest warm-upbounce managementsuppression listsunsubscribe best practicessender domain docs
Questions

About this page.

What is email deliverability?
Whether your email actually reaches the inbox, not just whether it was sent. A message can be accepted by the provider and still be filtered to spam or dropped, so deliverability measures real inbox placement — which is decided by authentication, reputation, list hygiene, engagement, and compliance.
How do I improve email deliverability?
Work the five pillars: authenticate with SPF/DKIM/DMARC, build and protect sender reputation, keep the list clean and verified, send relevant content that earns engagement, and stay compliant with unsubscribes and consent. Fix authentication and hygiene before tweaking content.
What's a good bounce and complaint rate?
Keep bounce rate under about 2% and spam-complaint rate under about 0.3% (Google's stated threshold for bulk senders). Crossing the complaint line is one of the fastest ways to wreck inbox placement, so make unsubscribing easy and verify lists before sending.
Why do my emails go to spam if they're being delivered?
"Delivered" only means the provider accepted the message — it can still route it to spam. That usually points to weak authentication, a cold or damaged sender reputation, low engagement, or a stale list. Fix those pillars rather than rewording the email.