Improving Email Deliverability

Deliverability is the difference between an email reaching the inbox and getting silently filtered into the spam folder - or rejected outright. Receiving servers like Gmail, Outlook, and Yahoo make that call in milliseconds based on a handful of signals you control.

This article is the short version. Each lever links to a deeper article when there is one.

1. Authenticate your domain

The single biggest predictor of inbox placement is whether your sending domain is properly authenticated. Three records work together:

  • SPF - tells receivers that Amazon SES is allowed to send for you. Set up via SES's Custom MAIL FROM domain.
  • DKIM - cryptographically signs each message. Mailblast and SES handle this automatically once you add the CNAME records during SES account setup.
  • DMARC - tells receivers what to do when an email fails SPF or DKIM, and sends you reports. See Enabling SPF and DMARC.

Without these, modern receivers will assume you are a spammer until proven otherwise. With them, you start on a level playing field.

2. Only send to people who asked

Sender reputation is built on engagement. The more your recipients open and click, the better your future emails land. The opposite is also true: subscribers who never asked to hear from you mark you as spam, and a handful of those is enough to tank your reputation.

The two practical rules:

3. Keep your list clean

Even a perfectly opted-in list decays - people change jobs, abandon addresses, and lose interest. Stale addresses bounce, and bounces hurt your sender reputation. Mailblast automatically removes hard bounces and complaints, but you should also:

  • Re-engage subscribers who have not opened anything in 6+ months with a "still want to hear from us?" campaign
  • Remove anyone who does not respond to that campaign
  • Watch for suspicious signup patterns (lots of similar-looking addresses) and clean them out

4. Watch your bounce and complaint rates

Amazon SES tracks two numbers across all your sending and will pause your account if they cross hard thresholds: 5% bounce rate and 0.1% complaint rate. See AWS SES bounce and complaint rates for what each one means and how to stay under them.

5. Write emails people want to read

The content matters less than people think, but it still matters:

  • From name and address: use a real human name and a recognisable sending domain - not noreply@. People mark emails from unfamiliar senders as spam.
  • Subject line: clear and specific beats clever and vague. Avoid all caps and excessive punctuation.
  • Body: keep a healthy ratio of text to images. Receivers are suspicious of image-only emails.
  • Unsubscribe link: visible and obvious. Hiding it just sends people to the spam button instead.

6. Warm up new sending

If you are about to send to a list of 50,000 people for the first time, do not send it all at once. Mailbox providers treat sudden volume from a new domain as suspicious. Send your first few campaigns to your most engaged segment (recent signups, active openers) and ramp from there over a few weeks.

The short checklist

If you do nothing else:

  • [ ] Domain verified with DKIM (CNAME records in DNS)
  • [ ] Custom MAIL FROM configured (SPF aligned)
  • [ ] DMARC record published with at least p=none
  • [ ] Unsubscribe link visible in every campaign
  • [ ] Subscriber list is fully opt-in
  • [ ] Bounce rate under 5%, complaint rate under 0.1%

Get those right and your emails land in the inbox the vast majority of the time.

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