> ## Documentation Index
> Fetch the complete documentation index at: https://openmail-docs-reputation-lifecycle-webhooks.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Email deliverability

> Best practices for landing outbound emails in the inbox. Covers IP warming, SPF/DKIM/DMARC alignment, content tips, and suppression handling.

Email deliverability is the art and science of getting your emails into your recipients' inboxes. It's not just about hitting "send" — it's about building a good reputation with email providers like Gmail and Outlook so they trust you're sending valuable content, not spam.

High deliverability is the key to successful email automation. This guide covers both your sending strategy and your email content.

### The technical foundation: SPF, DKIM, and DMARC

Before you send your first email, it's important to have the right technical foundation in place. SPF, DKIM, and DMARC are DNS records that act as a digital signature, proving to email providers that you are who you say you are.

<Tip>
  OpenMail handles SPF, DKIM, and DMARC automatically for `openmail.sh` — great for getting started. For high-volume cold outreach, verify your own custom domain (Developer plan and above). See [Custom domains](/concepts/custom-domains).
</Tip>

All inboxes use `openmail.sh` by default. For production outreach at scale, send from a verified custom domain like `outreach@yourcompany.com` so your reputation belongs to you.

<CardGroup>
  <Card title="Inboxes" icon="inbox" href="/concepts/inboxes">
    Learn about inbox address formats and how to configure your sending domain.
  </Card>
</CardGroup>

## High-volume sending strategy

How you send your emails is just as important as what you send. If you're sending a large volume of emails, follow these steps to build and maintain a strong sender reputation.

<Steps>
  <Step title="Warm up your inboxes">
    Don't go from zero to a thousand emails overnight. Email providers get
    suspicious of new inboxes that immediately send a high volume. Start slow
    and gradually increase your sending volume over several days or weeks. This
    "warm-up" process signals that you're a legitimate sender.

    <Note>
      **Example warm-up schedule:**

      * Day 1: 10 emails/inbox
      * Day 2: 20 emails/inbox
      * Day 3: 40 emails/inbox
      * ...and so on, doubling until you reach your target.
    </Note>

    See [Rate limits](/concepts/rate-limits) for per-inbox sending limits.
  </Step>

  <Step title="Distribute across inboxes">
    Instead of sending 10,000 emails from a single inbox, send 100 emails from
    100 different inboxes. This distributes your sending volume, reduces the
    risk of any single inbox getting flagged, and looks much more natural to
    email providers. OpenMail's ability to create inboxes at scale makes this
    easy to implement.

    <Warning>
      **Distribute on your domain.** Use multiple inboxes on a verified custom
      domain — one per agent, campaign, or [pod](/concepts/pods) tenant. Do
      not run high-volume cold outreach from shared `@openmail.sh` addresses.
    </Warning>

    <Note>
      **Reputation, not quota.** Inbox distribution protects per-inbox
      reputation and helps you stay under per-inbox daily limits. Your
      [account cold cap](/concepts/rate-limits) is shared across all inboxes —
      adding more inboxes does not multiply total cold volume. Upgrade your plan
      if you need a higher ceiling.
    </Note>
  </Step>

  <Step title="Protect your reputation">
    A domain's reputation is its most valuable asset. If you use a custom
    domain for outreach, consider rotating sending identities so a reputation
    hit on one doesn't impact the rest.
  </Step>
</Steps>

## High-impact content strategy

The content of your email plays a huge role in whether it's seen as a valuable message or as spam.

<Steps>
  <Step title="Personalize everything">
    Address your recipients by name in the subject line and email body. Use
    other data points you have to make the email feel like a one-to-one
    conversation, not a mass blast. Generic emails are a major red flag for spam
    filters.
  </Step>

  <Step title="Write like a human, not a marketer">
    Avoid "spammy" keywords (e.g., "free," "buy now," "limited time offer"),
    excessive exclamation points, and ALL CAPS. Write in a natural,
    conversational tone. The goal is to start a conversation, not to close a
    sale in the first email.
  </Step>

  <Step title="Skip images and tracking pixels">
    Images embedded in the email body set off spam filters. Open-tracking pixels
    are just tiny images encoded into the body — email providers know it. Drop
    them to improve deliverability.
  </Step>

  <Step title="Delay your links">
    Email providers are wary of links, especially in the first message of a
    conversation. Send your initial outreach with no links or images. Wait for
    the recipient to reply, and *then* send your call-to-action link. This
    looks like a natural conversation to providers.
  </Step>

  <Step title="Always include plain text">
    Email providers often flag HTML-only emails as spam. Including a plain text
    alternative demonstrates legitimacy and increases your chances of reaching
    the inbox.
  </Step>
</Steps>

## Suppressions

OpenMail automatically maintains a suppression list for bounces and spam complaints. Recipients who bounce or mark your email as spam are suppressed from future sends.

<CardGroup>
  <Card title="Suppressions" icon="ban" href="/concepts/suppressions">
    Learn how suppression lists work and how to manage them.
  </Card>
</CardGroup>

## What's next

<CardGroup cols={2}>
  <Card title="Rate limits" icon="gauge" href="/concepts/rate-limits">
    Per-inbox send limits and cold outreach throttling.
  </Card>

  <Card title="Idempotency" icon="repeat" href="/best-practices/idempotency">
    Safe retries so agents never send duplicate emails.
  </Card>

  <Card title="Inboxes" icon="inbox" href="/concepts/inboxes">
    Address formats, external IDs, and multi-tenant routing.
  </Card>

  <Card title="API reference" icon="code" href="/api-reference/introduction">
    Full endpoint documentation.
  </Card>
</CardGroup>