How to choose an email API in 2026: questions to ask six providers

An email API lets your application hand a message to a sending service over HTTP. Your code calls an endpoint with the recipient, subject and body. The provider then queues the message, signs it, delivers it to the mailbox provider and reports back what happened. You never run a mail server yourself.

SMTP relay does the same job over the older mail protocol. You point your app or framework at the provider's SMTP host with a username and password, and it relays the mail. SMTP is the easy choice when software already speaks it, such as a CMS, an ERP or a legacy app you cannot change. An HTTP API is usually the better choice for new code. It returns structured errors, works cleanly with retries, and pairs with webhooks that tell you about bounces and complaints. For which port to connect on, see our guide to SMTP ports.

Most providers on this list offer both. The choice between them rarely decides deliverability. What decides it is the infrastructure behind them and who else is sending through it.

Who else is on the shared pool. Every account starts on shared IPs unless it pays for dedicated ones. If a provider also sells marketing and bulk sending on that pool, your sign-in codes share reputation with promotions. Ask whether marketing and cold email are allowed on the IPs your transactional mail uses. If they are, ask whether the streams are separated.

How you move to isolation. At some volume, or when a security reviewer asks, you may want your own IPs or your own server. Check whether that is a setting on the same API or a separate product with a different integration. A migration you have to plan around is a migration you will put off.

Who runs the servers. When a reset email lands in spam, someone has to read the logs and change something. A provider that runs its own mail servers and IP space can do that directly. A reseller sending through someone else's infrastructure has to file a ticket with its own vendor. Security and procurement reviews ask the same question in writing: who handles this mail, and who handles it for them?

Authentication you can finish in an afternoon. Google, Yahoo and Microsoft expect SPF, DKIM and DMARC on mail you send. Any provider should walk you through the DNS records. Our SPF, DKIM and DMARC guide explains what each record does for transactional mail, and our guide to the Google, Yahoo and Microsoft sender rules covers the rules themselves.

Limits on a new account. Mailbox providers distrust sudden volume from a new sender, so most providers cap what a new account can send per day and raise the cap as you prove you send cleanly. If you are moving an existing app with real traffic, ask what the ramp looks like and who to contact to speed it up.

Price at the volume you will actually send. Starting prices tell you little. Price the plan at your volume today and at two or three times that, and check how overage is billed. A plan that is cheap at 50,000 emails can be expensive at 500,000.

The rest of the integration. Check for an SDK in your language, webhooks for delivery events, and inbound handling if your app needs to receive replies or parse incoming mail.

For a ranked list of providers with prices at 50,000, 100,000 and 1M emails, see the best transactional email APIs. Our comparison pages price Postmark, Resend, SendGrid, Mailgun and Amazon SES at volumes from 10,000 to 1M emails. Prices change, so check those breakdowns against each provider's own pricing page before you sign. The questions below are the ones that separate the providers once the prices are in front of you.

These are the list prices on Groundmail's pricing page, read on 2026-10-16. Overage is billed per 1,000 emails at the tier's rate.

Pro and Scale both list a 100,000 tier, and Pro is cheaper at that volume. Scale buys what Pro does not have: tiers up to 2.5M with overage falling to $0.46 per 1,000, up to 1,000 sending domains instead of Pro's 10, tenants for up to 1,000 of your own customers, and dedicated IPs. If you send 100,000 emails from one product and need none of that, Pro at $35 is the right plan.

At 1M emails a month, Scale costs $650 and includes your first dedicated IP, because the first IP is included from 500,000. On the Dedicated plan, the same 1M emails cost $299 plus 750,000 overage emails at $0.80 per 1,000, which comes to $899 a month. The extra cost buys a server of your own with no shared queue. That is usually a security or procurement requirement, not a deliverability one.

Every sending feature is on every plan, including inbound email, templates, automations and webhooks. A card on file is required to send, including on Free, and it is not charged unless you upgrade. Each accepted recipient message counts once, so a batch request is billed per message.

Most senders belong on a well-run shared pool. A dedicated IP only has a good reputation if you send enough steady volume to build one. Below that, a new dedicated IP can deliver worse than a clean shared pool. Our guide to shared vs dedicated IPs walks through where the line falls.

Move to a dedicated IP when your volume is steady and high, when your customers need fixed IPs to allowlist, or when you want reputation that is yours alone. Move to a dedicated server when a reviewer needs to know that no other sender's mail shares your queue. Groundmail's page on dedicated IPs and servers covers what each includes, such as warming before traffic moves over and reverse DNS on your own domain.

Do not pay for dedicated infrastructure on day one. Start on the pool and move when volume or a review calls for it.

New senders get a daily limit that grows as they prove they send cleanly. On Groundmail, paid accounts start at 1,000 product emails and 3,000 transactional emails a day. The limit doubles each day after you use at least half of it, as long as bounces stay under 2% and complaints under 0.1%. A clean sender goes from 1,000 to 64,000 a day in about a week. The ramp ends once it reaches your plan's monthly volume, and upgrading does not lift it. The Free plan stays at 100 a day.

The ramp exists because the IPs are shared. If you are moving an existing sender with real traffic and need more volume sooner, the pricing page says to email support@groundmail.dev. To move without dropping mail during the switch, see our guide to switching transactional email providers without downtime.

Groundmail is not for newsletters, marketing blasts or cold outreach. It sends only mail a user is waiting on: resets, sign-in codes, receipts, invitations and alerts. Marketing and cold email are not allowed on its IPs (AUP), and that rule is what keeps the shared pool clean.

If you need newsletters too, use a separate marketing service for them and keep them off your transactional path. Sending a promotion and a sign-in code through the same service and the same reputation means a bad campaign week can delay logins. Two vendors for two different jobs costs less than that.

Groundmail sends from mail servers and IP space it operates itself, keeps its shared pool to transactional mail only, and offers dedicated IPs and dedicated servers on the same API. It includes an HTTP API, SMTP relay, SDKs for Node, Python, Go, PHP and Ruby, a CLI and an MCP server. If you send password resets, receipts and alerts and want to know who else is on your pool, you can create your free account and send from the Free plan once your domain is verified.