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There are two ways to get email into Helo, and two types of email you can send. Understanding how these fit together will help you design your integration and get the most out of the platform.

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How you send: API vs SMTP

Helo accepts mail via two interfaces: API — the recommended approach for most use cases. You send a structured JSON request and get back immediate feedback on each message. It’s explicit, easy to debug, and gives you more control. SMTP — useful if you’re working with a tool or library that only speaks SMTP, or if you’re migrating from another provider and want minimal changes to your existing setup. Both interfaces support all of Helo’s mail types and features. If you’re starting fresh, the API is the way to go.

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What you send: Transactional vs. Broadcast

Helo uses separate infrastructure — separate API endpoints, queuing, and IP pools — for each mail type. This is one of the key ways we optimize deliverability for all emails you’ll send with us. When transactional and broadcast emails share the same sending IPs, inbox providers like Gmail can’t easily tell them apart. A newsletter that gets flagged as spam can drag down the reputation of the IPs it was sent from — and that hurts delivery of the password resets and order confirmations going out through those same IPs. Keeping them separated means your time-sensitive transactional messages stay fast and reliable, regardless of what’s happening on the broadcast side. Helo handles this separation automatically. You just tell us what type of email you’re sending, and we route it through the right infrastructure.

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Transactional email sending

Transactional emails are triggered by something a user did. The user is expecting the message immediately, and it needs to arrive fast. Common examples:
  • Account confirmations
  • Password resets
  • Invoices and payment receipts

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Sending infrastructure optimized for transactional emails

Helo delivers your transactional mail over infrastructure that’s optimized for exactly this use case, delivering your message as fast as possible. We generate and deliver your transactional messages immediately, and give you instant feedback on the validity and status of every email you send. See Transactional for more information on transactional mail sending.

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Broadcast email sending

Broadcasts are for sending the same message to a large list of recipients. No user action triggers them, you’re reaching out to your audience on your own schedule. Common examples:
  • Newsletters
  • Product update announcements
  • Promotional campaigns
Unlike transactional emails, broadcasts are first-class entities in Helo: they’re stored, queryable, and carry their own metrics (deliverability, engagement, opt-outs). This makes it easy to review how a campaign performed, track delivery progress, or get statistics for a specific send.

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Sending infrastructure optimized for broadcast emails

Helo processes Broadcasts asynchronously on dedicated infrastructure. Sending large amounts of email too quickly can cause deliverability issues, so we gradually process and deliver broadcasts at a rate that aims to prevent this from happening (while still ensuring messages land in the inbox quickly). The dedicated endpoint for sending broadcast email is POST /send/broadcast. Sending via the dedicated Broadcast endpoint also means you’re receiving additional metrics for your Broadcast send, including aggregated deliverability, engagement, or opt-out stats, helping you track overall campaign performance. You can also send a single broadcast message via POST /send/broadcast/message in case you want to send messages one-at-a-time, with immediate feedback, and don’t want any of the above features. And of course, you can also send single broadcast messages via SMTP. See Broadcasts for more information on broadcast mail sending.