Sendonis is an API-only email service launching soon, with EU-based sending and built-in deliverability guardrails. Join early access for an early-bird discount.

Introducing Sendonis: an email API with guardrails built in

Most applications need to send email. Password resets, sign-up confirmations, receipts, alerts and account notices all have to arrive, and they have to arrive quickly. Sending one email is easy. Sending thousands without hurting your domain's reputation, while keeping track of every bounce and complaint, takes more work than most teams expect.

We're building Sendonis for that job, and it's launching soon. It's a REST API running on EU-based sending infrastructure, with the deliverability safeguards we think every sender should have from day one. Early access is open now, and the first 100 confirmed sign-ups get an early-bird discount. Details are at the end of this post.

What Sendonis is

Sendonis is a multi-tenant platform for sending email through an API. When it launches, you'll verify your domain, create an API key and send messages with an HTTPS request. Sendonis will sign and send them, process what happens next and report the result back to you.

There are three parts:

Sending. A REST API that accepts your message, checks it against your suppression list and sends it from our EU-based infrastructure.
Feedback. Delivery, bounce and complaint events come back from receiving mail servers. Sendonis links each one to your account, updates your suppression list and forwards the event to your webhook.
Protection. Sendonis watches each account's bounce and complaint rates and pauses sending automatically if they go above safe limits.

That's the whole product. Sendonis won't try to be a newsletter builder or a CRM. It's the sending layer your application calls.

Why we're building it

Email deliverability depends on reputation, and reputation depends on behaviour. Mailbox providers look at whether your mail is authenticated, how often it bounces and how often recipients mark it as spam. A single bad import, like an old list or a typo-ridden CSV, can push those numbers up within hours. The damage to a domain's reputation can take weeks to repair.

Many sending setups leave the safeguards to you. You have to wire up bounce notifications, build a suppression table, remember to check it before every send, and watch your rates yourself. These are exactly the tasks that get skipped when a team is busy shipping product.

We want a service where those safeguards are part of sending, not optional extras.

What's included at launch

A REST API, and only an API

You'll send with an authenticated HTTPS request carrying a JSON body. There will be no SMTP relay and no SMTP credentials. That's a deliberate choice. Every message arrives through a path we can authenticate, validate and check against suppression before it's accepted. We explain the reasoning in Why Sendonis is API-only.

Your domain, properly authenticated

Before you can send, you'll verify your domain. Sendonis will give you DNS records for DKIM signing and a custom MAIL FROM subdomain with its own SPF record. With both in place, receiving servers can check that the message really came from you, and your mail can pass DMARC alignment under your own brand. You can prepare your DNS today with our guide: DKIM, SPF, DMARC and custom MAIL FROM, explained.

Automatic bounce and complaint handling

When a message hard-bounces, or a recipient marks it as spam, Sendonis will record the event and add the address to your account's suppression list. Every send is checked against that list, so you won't keep mailing addresses that will hurt you.

Per-tenant suppression lists

Every Sendonis account will have its own suppression list, kept apart from other customers' data. You'll be able to see which addresses are suppressed and why.

Event webhooks

Sendonis will send delivery, bounce and complaint events to an HTTPS endpoint you choose. Use them to mark an email address as invalid in your own database, show a delivery status in your admin panel, or alert your team when something looks wrong.

Sending-health protection

If an account's bounce rate goes above 4% or its complaint rate goes above 0.08%, Sendonis will pause sending for that account automatically. Pausing early, before mailbox providers or our sending infrastructure take action, protects your domain and everyone else on the platform. We wrote a separate post on why these two numbers matter.

Sending from the EU

All Sendonis email will be sent through EU-based sending infrastructure, dedicated to Sendonis and kept apart from other workloads. Delivery, bounce and complaint notifications will be handled in the EU too. For the full picture of where data is processed, including our own application hosting, see our Privacy Policy and Data Processing Agreement.

A strict policy, on purpose

A shared sending platform is only as good as its worst sender. That's why Sendonis has a strict Acceptable Use Policy:

Marketing email needs opt-in consent from each recipient.
Purchased, rented, shared or scraped lists are not allowed.
Every marketing email needs a working unsubscribe link and the sender's postal address.
Senders must use domains they control and have verified.

You are the sender, so consent and local rules are your responsibility. Depending on where your recipients are, that can mean GDPR in the EU, CAN-SPAM in the United States, or İYS registration for commercial electronic messages in Turkey. Sendonis gives you tools such as suppression, opt-out handling and authentication, but tools alone don't make sending lawful. If your business depends on mailing lists of unclear origin, Sendonis won't be the right fit, and we'd rather tell you that up front.

Who Sendonis is for

Sendonis will be a good fit if you:

build a web or mobile application that sends transactional email;
want to call an API rather than run or configure a mail server;
care about where your sending infrastructure runs and want it in the EU;
prefer a service that stops a bad send early to one that lets it run.

Join early access and get the early-bird offer

Sendonis is launching soon. Until then:

Join early access. It takes your email address and nothing else. Name and company are optional, and no payment card is needed.
Confirm your email address. We'll send you a confirmation link before launch. Only confirmed sign-ups keep their place.
Get the early-bird offer. The first 100 confirmed sign-ups get an early-bird discount for 2 months. Places go in order of original sign-up time, and only confirmed sign-ups count, so joining early helps.
Prepare your domain. Our DNS guide explains every record you'll publish, so you can be ready to send on day one.

Joining is free and doesn't commit you to anything. New accounts will start with conservative sending limits that grow as you build a sending history. Final prices will be published before launch on our pricing section.

If you have a use case we should support, or a question about whether Sendonis fits your project, we'd like to hear from you before launch. Join early access and we'll be in touch.