Hi HN, I'm Ryan, engineer and co-founder at Helo (https://www.helohq.com) - an email API for sending transactional and marketing email from your application: password resets, receipts, notifications, newsletters, etc.

Most of our team worked together at Postmark for many years, so we know what it takes to build a reliable email service. If you've ever loved a product and then watched it get acquired, you probably know the rest of that story. We started Helo to keep building the kind of product we're good at, improve on what we have learned, take good care of our customers, and stay independent while doing it. We're bootstrapped and plan to stay that way.

Helo covers everything you'd expect from a developer-focused email service:

- REST API and SMTP, with SDKs for Ruby, JS, C#, Python and Go (more to come) - Separate infrastructure for transactional and broadcast mail - Event logs, stats, webhooks, suppressions, unsubscribes, flexible permissions - Usage-based pricing with no arbitrary feature gates - https://www.helohq.com/pricing

Beyond the fundamentals, we've also put a lot of work into multi-tenant sending. When you're a platform sending on behalf of your own customers, you need to keep one bad sender from hurting everyone's deliverability, let customers send from their own domains, and keep stats and unsubscribes separate per customer.

We've built Helo to address all of these concerns, while also allowing flexibility in how the relationships between domains, webhooks, credentials, etc. are defined amongst your tenants. For example, you can share one verified domain across all your customers while letting a few use their own, send all events to one webhook or split them per tenant, and give tenants isolated credentials with permissions limited to exactly what they need.

If you've built multi-tenant sending before, what was most painful? Is there something you wish your email provider handled for you but doesn't? I'd love to hear about it.

Show HN: Helo – An email API from former Postmark folks