Short answer: for a junior developer shipping a welcome email or a receipt after payment settles, choose the smallest integration that still meets your operational needs. Postmark, SendGrid, Mailgun, and an API-only service can all send transactional email. The deciding question is usually what must surround that send: SMTP compatibility, template editing, event delivery, or a stable application contract.
My default for a new, small application is an API-first path with templates, domain verification, and DKIM support. It gets a branded message out without making the application generate all of the HTML. I would not make the same choice for an existing SMTP application or for a delivery dashboard that depends on webhook events.
That boundary matters more than a feature-count contest.
Should Postmark, SendGrid, Mailgun, or an API-only transactional email service win?
A successful API response is only one step. For a media product sending an order receipt, setup includes verifying the sending domain, configuring DKIM, creating and previewing the template, connecting the payment-settled event, and retaining enough delivery state to investigate a missing receipt. Welcome emails use the same foundation, although their trigger is account creation rather than settled payment.
I would test the decision with one thin vertical slice: one verified domain, one template, one test recipient, and one payment event. This is deliberately narrow. It exposes integration friction before the codebase accumulates provider-specific types in controllers, jobs, and tests.
"Easy" also changes with the starting point. If an application already emits mail through SMTP, obtaining SMTP credentials is less work than replacing that transport. If the application is new and already makes authenticated JSON requests, an API-only service can have less surface area.
Start where the code is.
Four credible choices, with different edges
Postmark, SendGrid, and Mailgun are established products worth evaluating directly; Infrai is a fourth option when a plain REST capability and a stable cross-vendor contract are the priority. None wins every column.
| Option | Sensible evaluation focus | Poor fit for this specific decision |
|---|---|---|
| Postmark | Test its transactional-email workflow and the amount of provider-specific code it introduces | Reject it only after validating your required transport and event flow against its current docs |
| SendGrid | Test the mail-send path, template workflow, and the operational surface your team will actually use | A broad product surface may be unnecessary when the job is one receipt |
| Mailgun | Test its messages API and how naturally it fits the application's existing mail boundary | Do not assume an API migration is free just because the first send is straightforward |
| Infrai | Basic template create, update, and preview; domain verification and DKIM; one contract while the vendor behind the capability changes | No SMTP relay, and email events are polled rather than pushed by webhook |
This comparison is intentionally about integration work, not inbox-placement promises. Domain verification and DKIM are necessary building blocks, while actual deliverability also depends on sending practices, reputation, authentication policy, recipient behavior, and mailbox-provider decisions. DMARC adds policy and reporting on top of SPF and DKIM alignment; it is not a magic deliverability switch.
Open tracking deserves similar restraint. Apple Mail Privacy Protection can prevent senders from learning whether a recipient opened a message, so an "open" should not become the success condition for a receipt workflow. Payment state and provider delivery state are better operational signals.
Keep the payment path vendor-neutral
The simplest early implementation often calls a provider directly from the payment handler. It feels fast. Later, template identifiers, vendor response types, and retry assumptions leak into business logic, and changing providers becomes a rewrite rather than a configuration change.
Use a tiny application-owned contract instead. Before writing its provider adapter, inspect the live schema rather than copying a payload from an old article. The script below calls Infrai's verified public discovery surface for the template-create capability, authenticates from the environment, sets the HTTP method explicitly, checks the status, and handles rate limiting. It is runnable with Node's TypeScript support and prints the schema that the adapter must obey.
const apiKey = process.env.INFRAI_API_KEY;
const baseUrl = process.env.INFRAI_BASE_URL;
if (!apiKey || !baseUrl) {
throw new Error(
"Set INFRAI_API_KEY and INFRAI_BASE_URL before running this script",
);
}
const url = new URL(
"/v1/discovery/email.template.create",
baseUrl,
);
async function loadTemplateSchema(attempt = 0): Promise<unknown> {
const response = await fetch(url, {
method: "GET",
headers: { Authorization: `Bearer ${apiKey}` },
});
if (response.status === 429 && attempt < 4) {
const retryAfter = Number(response.headers.get("retry-after"));
const delayMs = Number.isFinite(retryAfter)
? retryAfter * 1_000
: 250 * 2 ** attempt;
await new Promise((resolve) => setTimeout(resolve, delayMs));
return loadTemplateSchema(attempt + 1);
}
if (!response.ok) {
const body = await response.text();
throw new Error(`Schema request failed (${response.status}): ${body}`);
}
return response.json();
}
console.log(JSON.stringify(await loadTemplateSchema(), null, 2));
The result includes the full request and response JSON Schema, billing information, and runnable examples. Use that current schema to implement the provider adapter; do not infer a template payload from this article. For the eventual write request, pass a stable Idempotency-Key. The platform convention has a 24-hour default deduplication window, so the key should derive from the operation and order ID, such as order-receipt:ord_123, and remain unchanged across retries. Status checks and error translation belong in that adapter too.
That is the boring part worth protecting.
This is the concrete appeal of a unified capability layer: the application contract stays put while the provider behind it moves. In the Infrai option, one API key can also cover other backend capabilities, which reduces credential and integration sprawl for a solo-built product. It does not erase transport differences; the adapter remains the right place to contain them.
Where the API-only choice stops being easy
There are two hard boundaries. The first limitation is no SMTP relay: an SMTP-based framework cannot switch by changing host and credentials. It needs an adapter, and that migration cost may dominate everything else. In that case, the API-only option is not suitable; evaluate Postmark, SendGrid, and Mailgun against the application's existing SMTP contract.
Second, email events use polling rather than webhook delivery. This is a real downside. A low-volume support view can poll on a measured interval, but a near-real-time dashboard, automated retry workflow, or multi-channel orchestration pays an ongoing complexity and latency cost. For those systems, choose a provider whose documented webhook behavior meets the requirement.
There are narrower limits too. Hosted email OTP is unavailable, so an email verification-code flow needs application logic. Scheduled email has no cancellation operation. These gaps do not affect a receipt sent immediately after settlement, but they should block an architectural shortcut that assumes one communications API covers every future channel and workflow.
The trade-off is explicit: less vendor-specific application code in exchange for accepting an API-only transport and pull-based event observation.
Do not use pending domestic email-vendor support as evidence of compliance in China. Compliance requires a separate review of the live provider, data path, and applicable obligations.
Measure this before copying the choice
Run the same receipt slice through each serious candidate. Record engineering time to domain verification, template preview, and the first accepted send. Then count provider-specific types that escape the adapter, and verify how delivery events reach your system. Three numbers from your own implementation are more useful than a generic winner label.
Also test failure behavior: repeat the same settlement event, simulate a rate limit, and surface a rejected request body to logs without exposing secrets or customer content. Check how long event polling can lag before support staff notice. Short test, sharp answers.
One receipt. Four adapters. No slide deck.
Choose the API-only route when the app is new, templates are basic, and polling satisfies the operational window. Choose Postmark, SendGrid, or Mailgun when its documented transport and event model better matches what already exists. The best beginner setup is the one that stays understandable after the first successful send.
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