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Deliverability is whether your emails reach the inbox or the spam folder. It’s earned over time — mailbox providers score every sender on authentication, list quality, and how recipients react to their mail. Retainful automates much of this (suppression, unsubscribe handling, bounce processing), but the practices below are yours to own.

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1. Authenticate your domain

Non-negotiable. Verify your sending domain with DKIM, SPF, and DMARC before doing any meaningful volume. Gmail and Yahoo require authentication from bulk senders — without it, your mail may be rejected outright.

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2. Only email people who opted in

Every spam complaint hurts every future send. The complaint threshold mailbox providers tolerate is roughly 0.1–0.3% — one or two complaints per thousand emails.
  • Never buy, rent, or scrape lists.
  • Use double opt-in where quality matters more than volume.
  • Re-permission old lists before emailing them after a long gap.

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3. Keep your list clean

  • Retainful suppresses hard bounces, complaints, and unsubscribes automatically — don’t fight it.
  • Watch bounce rates per campaign; above ~2% means stale data.
  • Periodically sunset contacts who haven’t opened or clicked in 6–12 months — emailing the permanently disengaged drags down your reputation with everyone else.

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4. Send relevant mail at a steady rhythm

  • Segment instead of blasting — see Segments. Engagement (opens, clicks, replies) is the strongest positive signal a sender can earn.
  • Keep a consistent cadence; long silences followed by sudden bursts look like spam patterns.
  • If you’re moving to Retainful with a large list, warm up — start with your most engaged segment and widen over a couple of weeks.

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5. Mind your content

Content matters less than reputation, but it still matters:
  • Avoid ALL-CAPS subjects, excessive punctuation!!!, and walls of images with no text.
  • Keep your unsubscribe link obvious. Making it hard to leave converts unsubscribes into spam complaints — a far worse outcome.
  • Send a test to yourself and check where it lands before every major campaign.

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6. Monitor

Your campaign analytics tell the story: delivery rate sliding, opens collapsing on a specific mailbox provider, or bounce spikes are all early warnings. Catch them early and the fix is a cleanup; catch them late and it’s a slow reputation rebuild.
The compounding rule of deliverability: every send to an engaged subscriber makes the next send easier, and every send to a dead address makes it harder. Optimizing list quality beats optimizing send volume, every time.