Deliverability overview

Last updated: May 4, 2026

Deliverability is the percentage of your emails that reach the inbox rather than the spam folder or bouncing entirely. It's determined by a combination of technical setup, sending behavior, and email content.

Stamina handles the heavy lifting automatically — but understanding the key factors helps you maintain strong performance and diagnose issues quickly when they arise.

The four pillars of deliverability

1. DNS authentication

SPF, DKIM, and DMARC records tell receiving mail servers that your emails are legitimate and haven't been tampered with. Without these, emails are far more likely to land in spam or be rejected outright.

2. Domain and inbox warmup

New domains and inboxes need to build a sending reputation before handling full campaign volume. Stamina runs warmup automatically from day one, but it takes 2–4 weeks before an inbox is ready for high-volume sending.

3. Sending behavior

ISPs monitor patterns like sending volume spikes, bounce rates, and spam complaint rates. Consistent, predictable sending behavior with low bounce and complaint rates builds a positive reputation over time.

4. Email content

Spam filters analyze content. Heavy HTML formatting, excessive links, spam-trigger words, and large attachments all increase the chance of landing in spam. Plain-text or lightly formatted emails generally perform better for cold outreach.

How Stamina protects your deliverability

  • Provisions dedicated outreach domains separate from your primary brand domain — protecting your main domain's reputation

  • Configures SPF, DKIM, and DMARC automatically via DFY setup

  • Runs automatic inbox warmup from the moment inboxes are provisioned

  • Rotates sends across multiple inboxes to distribute load

  • Sets up email forwarding to your primary domain to generate positive engagement signals

Monitoring deliverability

Keep an eye on these metrics in your campaign analytics:

  • Bounce rate — Keep below 2%. Above this, ISPs start flagging your domain.

  • Open rate — Below 20% may indicate spam folder placement.

  • Spam complaint rate — Keep below 0.1%.

For external checks, use MXToolbox to verify DNS records and Mail Tester to score an email before launching.