Built for Developers. Designed for Teams.

Email Infrastructure for Modern Product Teams

Name: Keplars Mail Service
Brand: Keplars
Rating: 4.8 (150 reviews)

Keplars powers transactional and marketing emails with full delivery visibility, sandbox testing, and seamless scale - with strong developer experience, enabling you to send emails in under 5 clicks, and usage-based pricing.

< 5s Average Time to Inbox

Delivered fast via optimized infrastructure and multi-region routing.

99.77% Deliverability Rate

SPF, DKIM, DMARC-ready with trusted providers for maximum inbox placement.

100% Delivery Transparency

Track delivery, opens, clicks, and full email timelines in one place.

Trusted by world-class developers & industry leading teams

AWS - Amazon Web Services uses Keplars transactional email API

FoundersBoxx - startup platform using Keplars email infrastructure

GitStart - developer platform powered by Keplars email API

Microsoft - enterprise team using Keplars transactional email service

Roostoo - fintech app sending emails via Keplars

Supabase - open source backend using Keplars email delivery

Touchstack - product team using Keplars for transactional emails

"Keplars made email much easier for us. We've used other email tools before, and there's usually some friction - setup, deliverability, or configuration. With Keplars, things felt much more straightforward. We got started quickly, and emails have been consistently reliable. Deliverability has been strong, and the platform is built with strong security, so we're comfortable using it for critical user communication. The developer experience is smooth, and the email editor makes it easy to build and iterate without switching tools. Overall, it fits naturally into our product workflow."

Hamza Zia

Founder & CEO at Gitstart

"We tried a few email tools before this, and honestly, the biggest difference for us was how simple everything felt. You don't need to spend hours figuring things out. The APIs are clear, and the email editor is one of the easiest we've used. It's powerful, but not overwhelming."

Edward So

Cofounder and CEO @ Roostoo Labs

"Keplars runs our internal transactional emails and powers email sending for FoundersBoxx users directly from their own accounts. Two very different use cases, one clean integration. Had it all wired up in minutes."

Filiberto Secchi

Founder & CEO at FoundersBoxx

"From a sales and customer communication perspective, reliability and visibility matter a lot. With Keplars, we can clearly see delivery, opens, and clicks without digging through logs or multiple tools. It's straightforward, fast to set up, and doesn't require constant maintenance. Compared to other platforms we've used, it just feels more predictable and easier to work with."

Damien Mahuzier

Head of Sales at Gitstart

Built to Work With Any Stack

One unified API and SDK suite that adapts to your language, framework, and workflow. Designed for developers in every ecosystem - from web apps to mobile to backend systems.

api-request.sh

1curl --request POST \
2  --url https://api.keplars.com/api/v1/send-email/instant \
3  --header 'Authorization: Bearer kms_3725865b5eee62f0.*******************************' \
4  --header 'content-type: application/json' \
5  --data '{
6  "to": [
7    "[email protected]"
8  ],
9  "subject": "Your 2FA Code",
10  "body": "<b>Your verification code is: 123456</b>"
11}'

send-email.js

1const axios = require('axios');
2
3const client = axios.create({
4  baseURL: 'https://api.keplars.com',
5  headers: {
6    'Authorization': 'Bearer kms_3725865b5eee62f0.*******************************'
7  }
8});
9
10await client.post('/api/v1/send-email/instant', {
11  to: ['[email protected]'],
12  subject: 'Your 2FA Code',
13  body: '<b>Your verification code is: 123456</b>',
14  is_html: true
15});

What is OAuth Email Domain?

Connect your Google Workspace, Gmail, or Microsoft Outlook account and start sending transactional emails in minutes. Customize the sender name to match your product, with no DNS, SPF, or DKIM configuration. Designed for teams who want to move fast first, and add custom domains later when it actually makes sense.

Let's count the clicks

Click 1

Connect your Email account securely with OAuth authentication via Gmail/Workspace or Microsoft Outlook to enable email sending.

Know Exactly What Happens After You Send

Track every email from delivery to engagement with complete visibility. See delivery status, open events, link clicks, and detailed timelines - all in one place.

No more guesswork, no scattered logs. Just clear insight into how your emails perform and how users interact with them.

Track Deliverability

SUBJECTRECIPIENTSSTATUS

Welcome Email[email protected]

Sent

Newsletter Template (Visual)...[email protected]

delivered

Password Reset OTP[email protected]

delivered Opened

RECIPIENTS

[email protected]

EMAIL CONTENT

Nexio

Password Reset OTP

Hi Alex, use the OTP below to reset your password. It expires in 10 minutes.

Your one-time password

482 917

Reset Password →

If you didn't request this, please ignore this email or contact support if you have concerns.

Nexio Inc. · Security Team

DELIVERY TIMELINE

Queued

Email accepted and added to queue

3/20/2026, 3:56:39 PM

Sent+< 1s

Handed off to email provider

3/20/2026, 3:56:39 PM

Delivered+< 1s

Confirmed receipt by mail server

3/20/2026, 3:56:39 PM

Opened+10s

Recipient opened the email

3/20/2026, 3:56:49 PM

Clicked+19s

Recipient clicked a link

3/20/2026, 3:57:07 PM

Integrate Once - Every Email Format, Every Loved Tool

From Firebase triggers to Vercel edge functions, and from React Email to Handlebars - Keplars slots into your stack without changing how you build.

Read Documentation

Email on auth events & Firestore triggers.

Add email to your app, no SMTP needed.

Send emails from Next.js routes or edge functions.

Email on auth flows & real-time database events.

Email on auth events & Firestore triggers.

Add email to your app, no SMTP needed.

Send emails from Next.js routes or edge functions.

Email on auth flows & real-time database events.

Build responsive emails with a clean markup language.

Write templates with expressive Pug syntax.

Craft emails using familiar React components.

Dynamic content with Handlebars expressions.

Generate email HTML with embedded JavaScript.

Build responsive emails with a clean markup language.

Write templates with expressive Pug syntax.

Craft emails using familiar React components.

Dynamic content with Handlebars expressions.

Generate email HTML with embedded JavaScript.

Build responsive emails with a clean markup language.

Write templates with expressive Pug syntax.

Craft emails using familiar React components.

Dynamic content with Handlebars expressions.

Generate email HTML with embedded JavaScript.

Build responsive emails with a clean markup language.

Write templates with expressive Pug syntax.

Craft emails using familiar React components.

Dynamic content with Handlebars expressions.

Generate email HTML with embedded JavaScript.

New Feature

Send emails from a domain you trust

Start instantly with an OAuth email managed domain, or switch to your own custom domain when you're ready. Managed domains work out of the box, while custom domains give you full control when you need it - without changing your integration.

The Sandbox
Your Email System Needs

Validate templates, triggers, and flows in a controlled environment, without affecting users, reputation, or your sending quota.

Explore Sandbox

Every production system has a staging environment. Your email should too.

[email protected]

No emails are sent to real users

Sandbox runs don't count toward your quota

Validate templates, logic, and triggers

Full visibility before production

LaunchPad
- Where Every Email Begins

Just drag and drop or craft your perfect AI-powered transactional email in minutes.
Your No-code email templates are here!

Create and manage all your email templates in one place.
Generate templates instantly with AI - just describe what you need.
Choose from ready-made templates for OTPs, receipts, and more.
Edit HTML visually or in code - changes reflect instantly.
Save and reuse templates across projects.
Preview emails across devices before sending.

Watch Demo Video

schedule-email.sh

1curl -X POST https://api.keplars.com/api/v1/send-email/schedule \
2  -H "Authorization: Bearer YOUR_API_KEY" \
3  -H "Content-Type: application/json" \
4  -d '{
5    "scheduled_at": "2026-01-25_09:00:00",
6    "timezone": "UTC",
7    "email": {
8      "from": "[email protected]",
9      "from_name": "Customer Success Team",
10      "to": ["[email protected]"],
11      "template_id": "019a83de-2fc2-7b5f-bfbc-c951fe1200f7",
12      "params": {
13        "customerName": "John Doe",
14        "eventDate": "February 1st, 2026"
15      }
16    }
17  }'

Schedule
Your Emails

Send emails at the perfect moment with our powerful scheduling API. Whether it's a welcome series, appointment reminders, or time-sensitive notifications, schedule your transactional emails to arrive exactly when your users need them.

Schedule emails for any future date and time with timezone support.
Use your saved templates with dynamic parameters.
Cancel or modify scheduled emails anytime before delivery.

View Documentation

Developer-friendly email API with SDKs and webhooks for multiple languages

Hassle-Free Setup

No SMTP configs, no app passwords, no DNS headaches. Connect Gmail or Google Workspace instantly with secure authentication.

01 / 04

Developer-First Experience

Send emails via clean APIs, SDKs, and Webhooks - ready for almost every language. Simple, well-documented, and built for developers.

02 / 04

Enterprise-Grade Security

Bank-level encryption and role-based access control (RBAC) keep your email delivery safe, compliant, and protected.

03 / 04

Scalable & Reliable Delivery

Send from hundreds to millions of transactional emails with 99.9% uptime. Auto-scaling infrastructure that grows with your needs.

04 / 04

Built for Deliverability, Not Headaches

The core capabilities that make Keplars a reliable transactional email engine.

Inbox Delivery Rate

No SMTP or app password issues

99.77%

Faster Onboarding

Compared to traditional SMTP setups

10x

Fewer Failed Deliveries

No DNS misconfigurations blocking your mail

70%

Reputation Score

Trusted sender rating, inbox confidence every time you send

A+

Setup Time

API & SMTP keys, Webhooks, no server configs required

<5 min

Developer-Friendly

Webhooks, SDKs, API driven, detailed logs & analytics

Dev-First

Custom Domain Ready

No email provider lock-in - bring your own domain. SPF + DKIM + DMARC Verified

Verified

Multi-Provider Flexibility

Use Gmail, Workspace, Outlook, or your own domain. Switch anytime.

4-Layer

AI-Powered Templates

Build editable, send-ready transactional emails in seconds with smart variables and full HTML control.

Launchpad

Keplars
is the confidence you need in a transactional mail provider

Switching to a new email service doesn't have to be risky or complicated. With Keplars Mail Service, you get instant setup, enterprise-grade security, and proven inbox deliverability - without the hassle of SMTP or app passwords.

We built Keplars to give developers and teams the confidence that every critical email - password reset, invoice, or alert - lands safely in the inbox.

See what makes Keplars different:

99.9% Uptime

Trusted by thousands of developers

897 more

10M+

Emails Delivered

5k+

Active Users

99.77%

Inbox Rate

What drives us

Keplars is removing friction from email infrastructure for transactional and product emails, giving developers a predictable, boring email-sending foundation, without ongoing setup or debugging - so teams can focus on the product, not email infrastructure.

I've tried several email APIs, but Keplars.com stands out with its simplicity and speed. Perfect for high-volume transactional emails without the hassle. Top-notch service!

Anchit Das

Co-Founder & CTO @ Stealth AI Startup

Very cool! Thanks for the video that was well made and helpful.

Jonathan Goldsmith

iOS Developer

I really love how you've removed the pain point for developer when configuring a mail service like resend, where I always need to have a domain registered already that I can map to the service.

Sola Maxwell Lana

Full-stack Developer

Have been using other service in the past, I guess a simple REST bases system is much better. I like the product.

Priyanshu Verma

Co-Founder & Tech @KaizenLabs

Keplars made setting up email for our startup product straightforward and fast. From a backend perspective, the API was clear and developer-friendly, and we had everything running within minutes.

Oluwatobi Makinde

Lead Software Developer

I really like what you’ve built, the user experience is very intuitive. The setup process was smooth and straightforward.

Collins Ndubisi

Product Designer & Game Developer

I switched from EmailJS to Keplars to focus on code rather than configurations. The instant open and delivery rate tracking gives me total confidence, plus the AI templates save me hours of design work. It is the best choice for developers who value efficiency over complex setups.

Joseph Jonah

Full-Stack Developer

I've tried several email APIs, but Keplars.com stands out with its simplicity and speed. Perfect for high-volume transactional emails without the hassle. Top-notch service!

Anchit Das

Co-Founder & CTO @ Stealth AI Startup

Very cool! Thanks for the video that was well made and helpful.

Jonathan Goldsmith

iOS Developer

I really love how you've removed the pain point for developer when configuring a mail service like resend, where I always need to have a domain registered already that I can map to the service.

Sola Maxwell Lana

Full-stack Developer

Have been using other service in the past, I guess a simple REST bases system is much better. I like the product.

Priyanshu Verma

Co-Founder & Tech @KaizenLabs

Keplars made setting up email for our startup product straightforward and fast. From a backend perspective, the API was clear and developer-friendly, and we had everything running within minutes.

Oluwatobi Makinde

Lead Software Developer

I really like what you’ve built, the user experience is very intuitive. The setup process was smooth and straightforward.

Collins Ndubisi

Product Designer & Game Developer

Joseph Jonah

Full-Stack Developer

Have been using other service in the past, I guess a simple REST bases system is much better. I like the product.

Priyanshu Verma

Co-Founder & Tech @KaizenLabs

Keplars made setting up email for our startup product straightforward and fast. From a backend perspective, the API was clear and developer-friendly, and we had everything running within minutes.

Oluwatobi Makinde

Lead Software Developer

I really like what you’ve built, the user experience is very intuitive. The setup process was smooth and straightforward.

Collins Ndubisi

Product Designer & Game Developer

Joseph Jonah

Full-Stack Developer

Lightning-fast support and continuous improvements. Excellent service.

James Brown

DevOps Engineer

Seamless workflow integration that saved us countless hours.

Lisa Anderson

Full Stack Developer

Professional, reliable, and feature-rich. Everything we needed in one place.

Christopher Lee

Tech Lead

Have been using other service in the past, I guess a simple REST bases system is much better. I like the product.

Priyanshu Verma

Co-Founder & Tech @KaizenLabs

Keplars made setting up email for our startup product straightforward and fast. From a backend perspective, the API was clear and developer-friendly, and we had everything running within minutes.

Oluwatobi Makinde

Lead Software Developer

I really like what you’ve built, the user experience is very intuitive. The setup process was smooth and straightforward.

Collins Ndubisi

Product Designer & Game Developer

Joseph Jonah

Full-Stack Developer

Lightning-fast support and continuous improvements. Excellent service.

James Brown

DevOps Engineer

Seamless workflow integration that saved us countless hours.

Lisa Anderson

Full Stack Developer

Professional, reliable, and feature-rich. Everything we needed in one place.

Christopher Lee

Tech Lead

Joseph Jonah

Full-Stack Developer

Lightning-fast support and continuous improvements. Excellent service.

James Brown

DevOps Engineer

Seamless workflow integration that saved us countless hours.

Lisa Anderson

Full Stack Developer

Professional, reliable, and feature-rich. Everything we needed in one place.

Christopher Lee

Tech Lead

I've tried several email APIs, but Keplars.com stands out with its simplicity and speed. Perfect for high-volume transactional emails without the hassle. Top-notch service!

Anchit Das

Co-Founder & CTO @ Stealth AI Startup

Very cool! Thanks for the video that was well made and helpful.

Jonathan Goldsmith

iOS Developer

I really love how you've removed the pain point for developer when configuring a mail service like resend, where I always need to have a domain registered already that I can map to the service.

Sola Maxwell Lana

Full-stack Developer

Joseph Jonah

Full-Stack Developer

Lightning-fast support and continuous improvements. Excellent service.

James Brown

DevOps Engineer

Seamless workflow integration that saved us countless hours.

Lisa Anderson

Full Stack Developer

Professional, reliable, and feature-rich. Everything we needed in one place.

Christopher Lee

Tech Lead

I've tried several email APIs, but Keplars.com stands out with its simplicity and speed. Perfect for high-volume transactional emails without the hassle. Top-notch service!

Anchit Das

Co-Founder & CTO @ Stealth AI Startup

Very cool! Thanks for the video that was well made and helpful.

Jonathan Goldsmith

iOS Developer

I really love how you've removed the pain point for developer when configuring a mail service like resend, where I always need to have a domain registered already that I can map to the service.

Sola Maxwell Lana

Full-stack Developer

Start sending transactional emails with Keplars — developer-first email API

Ready to take your emails beyond the stratosphere?

Keplars is your launchpad to effortless emailing.

Email Infrastructure for Modern Product Teams

Trusted by world-class developers & industry leading teams

Built to Work With Any Stack

What is OAuth Email Domain?

Click 1

Click 1

Click 2

Click 3

Click 4

Know Exactly What Happens After You Send

Integrate Once - Every Email Format, Every Loved Tool

Send emails from a domain you trust

The Sandbox Your Email System Needs

LaunchPad - Where Every Email Begins

Schedule Your Emails

Key Features — Hassle-Free Setup, Developer-First Experience, Enterprise Security, Scalable Delivery

Hassle-Free Setup

Developer-First Experience

Enterprise-Grade Security

Scalable & Reliable Delivery

Built for Deliverability, Not Headaches

Inbox Delivery Rate

Faster Onboarding

Fewer Failed Deliveries

Reputation Score

Setup Time

Developer-Friendly

Custom Domain Ready

Multi-Provider Flexibility

AI-Powered Templates

Keplars is the confidence you need in a transactional mail provider

See what makes Keplars different:

99.9% Uptime

What drives us

Ready to take your emails beyond the stratosphere?

Solutions

Company

Resources

Compare

Help

Legal

Built to Work With Any Stack

What is OAuth Email Domain?

Click 1

Click 1

Click 2

Click 3

Click 4

Know Exactly What Happens After You Send

Integrate Once - Every Email Format, Every Loved Tool

Send emails from a domain you trust

The Sandbox Your Email System Needs

LaunchPad - Where Every Email Begins

Schedule Your Emails

Key Features — Hassle-Free Setup, Developer-First Experience, Enterprise Security, Scalable Delivery

Hassle-Free Setup

Developer-First Experience

Enterprise-Grade Security

Scalable & Reliable Delivery

Built for Deliverability, Not Headaches

Inbox Delivery Rate

Faster Onboarding

Fewer Failed Deliveries

Reputation Score

Setup Time

Developer-Friendly

Custom Domain Ready

Multi-Provider Flexibility

AI-Powered Templates

Keplars is the confidence you need in a transactional mail provider

See what makes Keplars different:

99.9% Uptime

Ready to take your emails beyond the stratosphere?

The Sandbox
Your Email System Needs

LaunchPad
- Where Every Email Begins

Schedule
Your Emails

Keplars
is the confidence you need in a transactional mail provider

The Sandbox
Your Email System Needs

LaunchPad
- Where Every Email Begins

Schedule
Your Emails

Keplars
is the confidence you need in a transactional mail provider