Send Email

Priority queue endpoints for sending email. Choose the endpoint that matches the urgency of your email.

Endpoints

Method	Endpoint	Priority	Delivery
`POST`	`/send-email/instant`	Instant	0-5 sec
`POST`	`/send-email/high`	High	0-30 sec
`POST`	`/send-email/async`	Normal	0-5 min
`POST`	`/send-email/bulk`	Low	Idle
`POST`	`/send-email/schedule`	Scheduled	Future time

Default to /send-email/async. Only escalate when real-time delivery genuinely matters.

Request Body

{
  "to": ["[email protected]"],
  "subject": "Your order is confirmed",
  "body": "<h1>Thanks for your order!</h1>",
  "from": "[email protected]",
  "from_name": "Acme Store",
  "reply_to": "[email protected]",
  "cc": ["[email protected]"],
  "bcc": ["[email protected]"]
}

Fields

Field	Type	Required	Notes
`to`	`string[]`	Yes	Recipient addresses
`subject`	`string`	Yes*	Required unless using `template_id`
`body`	`string`	Yes*	HTML or plain text. Required unless using `template_id`
`from`	`string`	Conditional	Required when using a custom domain or SMTP credential
`from_name`	`string`	No	Display name for sender
`reply_to`	`string`	No	Reply-to address
`cc`	`string[]`	No	CC recipients
`bcc`	`string[]`	No	BCC recipients
`template_id`	`UUID`	No	Use instead of `subject` + `body`
`params`	`object`	No	Handlebars variables for `template_id`

Template Email

Use template_id + params instead of subject and body. Do not send both.

{
  "to": ["[email protected]"],
  "template_id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "params": {
    "firstName": "Alice",
    "resetLink": "https://..."
  }
}

Scheduled Email

Add scheduled_at and timezone to any send-email body when using the /schedule endpoint:

{
  "to": ["[email protected]"],
  "subject": "Your weekly digest",
  "body": "<p>Here is what happened this week.</p>",
  "scheduled_at": "2025-12-25_09:00:00",
  "timezone": "America/New_York"
}

Field	Format	Notes
`scheduled_at`	`YYYY-MM-DD_HH:MM:SS` or ISO 8601	Min 1 minute ahead, max 365 days
`timezone`	IANA timezone string	e.g. `UTC`, `Europe/London`

Requires LAUNCH plan or higher.

Response

{
  "success": true,
  "message": "Email queued successfully",
  "email_id": "em_7f3a9b2c1d4e",
  "queue": "async",
  "estimated_delivery": "0-5 minutes"
}

Examples

Async (normal priority)

curl -X POST "https://api.keplars.com/api/v1/send-email/async" \
  -H "Authorization: Bearer $KEPLARS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"to":["[email protected]"],"subject":"Hello from Keplars","body":"Your first API email!"}'

const res = await fetch(
  'https://api.keplars.com/api/v1/send-email/async',
  {
    method: 'POST',
    headers: {
      Authorization: `Bearer ${process.env.KEPLARS_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
    to: ['[email protected]'],
    subject: 'Hello from Keplars',
    body: 'Your first API email!',
  }),
  },
);
const { data } = await res.json();

import requests, os
res = requests.post(
    'https://api.keplars.com/api/v1/send-email/async',
    json={
        'to': ['[email protected]'],
        'subject': 'Hello from Keplars',
        'body': 'Your first API email!',
    },
    headers={'Authorization': f'Bearer {os.environ["KEPLARS_API_KEY"]}'},
)
data = res.json()['data']

package main

import (
    "bytes"
    "fmt"
    "io"
    "net/http"
    "os"
)

func main() {
    body := bytes.NewBufferString(`{"to":["[email protected]"],"subject":"Hello from Keplars","body":"Your first API email!"}`)
    req, _ := http.NewRequest("POST",
        "https://api.keplars.com/api/v1/send-email/async", body)
    req.Header.Set("Authorization", "Bearer "+os.Getenv("KEPLARS_API_KEY"))
    req.Header.Set("Content-Type", "application/json")
    resp, _ := (&http.Client{}).Do(req)
    defer resp.Body.Close()
    b, _ := io.ReadAll(resp.Body)
    fmt.Println(string(b))
}

<?php
$ch = curl_init('https://api.keplars.com/api/v1/send-email/async');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_POST           => true,
    CURLOPT_POSTFIELDS     => json_encode([
        'to' => ['[email protected]'],
        'subject' => 'Hello from Keplars',
        'body' => 'Your first API email!',
    ]),
    CURLOPT_HTTPHEADER     => [
        'Authorization: Bearer ' . getenv('KEPLARS_API_KEY'),
        'Content-Type: application/json',
    ],
]);
$data = json_decode(curl_exec($ch), true)['data'];
curl_close($ch);

using System.Net.Http;
using System.Net.Http.Json;

var client = new HttpClient();
client.DefaultRequestHeaders.Add(
    "Authorization", $"Bearer {Environment.GetEnvironmentVariable("KEPLARS_API_KEY")}"
);
var response = await client.PostAsJsonAsync(
    "https://api.keplars.com/api/v1/send-email/async",
    new
{
    to = new[] { "[email protected]" },
    subject = "Hello from Keplars",
    body = "Your first API email!"
}
);
var body = await response.Content.ReadAsStringAsync();

use reqwest::Client;
use serde_json::json;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();
    let res = client
        .post("https://api.keplars.com/api/v1/send-email/async")
        .header("Authorization", format!("Bearer {}", std::env::var("KEPLARS_API_KEY")?))
        .json(&json!({
    "to": [
        "[email protected]"
    ],
    "subject": "Hello from Keplars",
    "body": "Your first API email!"
}))
        .send()
        .await?;
    let data: serde_json::Value = res.json().await?;
    println!("{}", data);
    Ok(())
}

#include <curl/curl.h>
#include <cstdlib>
#include <string>

int main() {
    CURL* curl = curl_easy_init();
    std::string auth = std::string("Authorization: Bearer ") + std::getenv("KEPLARS_API_KEY");
    const char* payload = "{\"to\":[\"[email protected]\"],\"subject\":\"Hello from Keplars\",\"body\":\"Your first API email!\"}";
    struct curl_slist* headers = nullptr;
    headers = curl_slist_append(headers, auth.c_str());
    headers = curl_slist_append(headers, "Content-Type: application/json");
    curl_easy_setopt(curl, CURLOPT_URL, "https://api.keplars.com/api/v1/send-email/async");
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, payload);
    curl_easy_perform(curl);
    curl_slist_free_all(headers);
    curl_easy_cleanup(curl);
}

#include <curl/curl.h>
#include <stdio.h>
#include <stdlib.h>

int main(void) {
    CURL* curl = curl_easy_init();
    char auth[256];
    snprintf(auth, sizeof(auth), "Authorization: Bearer %s", getenv("KEPLARS_API_KEY"));
    const char* payload = "{\"to\":[\"[email protected]\"],\"subject\":\"Hello from Keplars\",\"body\":\"Your first API email!\"}";
    struct curl_slist* headers = NULL;
    headers = curl_slist_append(headers, auth);
    headers = curl_slist_append(headers, "Content-Type: application/json");
    curl_easy_setopt(curl, CURLOPT_URL, "https://api.keplars.com/api/v1/send-email/async");
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, payload);
    curl_easy_perform(curl);
    curl_slist_free_all(headers);
    curl_easy_cleanup(curl);
    return 0;
}

Instant (highest priority)

curl -X POST "https://api.keplars.com/api/v1/send-email/instant" \
  -H "Authorization: Bearer $KEPLARS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"to":["[email protected]"],"subject":"Your verification code","body":"Your code: 123456"}'

const res = await fetch(
  'https://api.keplars.com/api/v1/send-email/instant',
  {
    method: 'POST',
    headers: {
      Authorization: `Bearer ${process.env.KEPLARS_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
    to: ['[email protected]'],
    subject: 'Your verification code',
    body: 'Your code: 123456',
  }),
  },
);
const { data } = await res.json();

import requests, os
res = requests.post(
    'https://api.keplars.com/api/v1/send-email/instant',
    json={
        'to': ['[email protected]'],
        'subject': 'Your verification code',
        'body': 'Your code: 123456',
    },
    headers={'Authorization': f'Bearer {os.environ["KEPLARS_API_KEY"]}'},
)
data = res.json()['data']

package main

import (
    "bytes"
    "fmt"
    "io"
    "net/http"
    "os"
)

func main() {
    body := bytes.NewBufferString(`{"to":["[email protected]"],"subject":"Your verification code","body":"Your code: 123456"}`)
    req, _ := http.NewRequest("POST",
        "https://api.keplars.com/api/v1/send-email/instant", body)
    req.Header.Set("Authorization", "Bearer "+os.Getenv("KEPLARS_API_KEY"))
    req.Header.Set("Content-Type", "application/json")
    resp, _ := (&http.Client{}).Do(req)
    defer resp.Body.Close()
    b, _ := io.ReadAll(resp.Body)
    fmt.Println(string(b))
}

<?php
$ch = curl_init('https://api.keplars.com/api/v1/send-email/instant');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_POST           => true,
    CURLOPT_POSTFIELDS     => json_encode([
        'to' => ['[email protected]'],
        'subject' => 'Your verification code',
        'body' => 'Your code: 123456',
    ]),
    CURLOPT_HTTPHEADER     => [
        'Authorization: Bearer ' . getenv('KEPLARS_API_KEY'),
        'Content-Type: application/json',
    ],
]);
$data = json_decode(curl_exec($ch), true)['data'];
curl_close($ch);

using System.Net.Http;
using System.Net.Http.Json;

var client = new HttpClient();
client.DefaultRequestHeaders.Add(
    "Authorization", $"Bearer {Environment.GetEnvironmentVariable("KEPLARS_API_KEY")}"
);
var response = await client.PostAsJsonAsync(
    "https://api.keplars.com/api/v1/send-email/instant",
    new
{
    to = new[] { "[email protected]" },
    subject = "Your verification code",
    body = "Your code: 123456"
}
);
var body = await response.Content.ReadAsStringAsync();

use reqwest::Client;
use serde_json::json;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();
    let res = client
        .post("https://api.keplars.com/api/v1/send-email/instant")
        .header("Authorization", format!("Bearer {}", std::env::var("KEPLARS_API_KEY")?))
        .json(&json!({
    "to": [
        "[email protected]"
    ],
    "subject": "Your verification code",
    "body": "Your code: 123456"
}))
        .send()
        .await?;
    let data: serde_json::Value = res.json().await?;
    println!("{}", data);
    Ok(())
}

#include <curl/curl.h>
#include <cstdlib>
#include <string>

int main() {
    CURL* curl = curl_easy_init();
    std::string auth = std::string("Authorization: Bearer ") + std::getenv("KEPLARS_API_KEY");
    const char* payload = "{\"to\":[\"[email protected]\"],\"subject\":\"Your verification code\",\"body\":\"Your code: 123456\"}";
    struct curl_slist* headers = nullptr;
    headers = curl_slist_append(headers, auth.c_str());
    headers = curl_slist_append(headers, "Content-Type: application/json");
    curl_easy_setopt(curl, CURLOPT_URL, "https://api.keplars.com/api/v1/send-email/instant");
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, payload);
    curl_easy_perform(curl);
    curl_slist_free_all(headers);
    curl_easy_cleanup(curl);
}

#include <curl/curl.h>
#include <stdio.h>
#include <stdlib.h>

int main(void) {
    CURL* curl = curl_easy_init();
    char auth[256];
    snprintf(auth, sizeof(auth), "Authorization: Bearer %s", getenv("KEPLARS_API_KEY"));
    const char* payload = "{\"to\":[\"[email protected]\"],\"subject\":\"Your verification code\",\"body\":\"Your code: 123456\"}";
    struct curl_slist* headers = NULL;
    headers = curl_slist_append(headers, auth);
    headers = curl_slist_append(headers, "Content-Type: application/json");
    curl_easy_setopt(curl, CURLOPT_URL, "https://api.keplars.com/api/v1/send-email/instant");
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, payload);
    curl_easy_perform(curl);
    curl_slist_free_all(headers);
    curl_easy_cleanup(curl);
    return 0;
}

Manage Scheduled Emails

GET  /send-email/scheduled
DELETE /send-email/schedule/:id

Send Email

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