The unified email API, with better logs, retries, and integrations.

Unified Email API

Pop in your API keys and you'll be sending email in minutes through SendGrid, Mailgun, Amazon SES, SparkPost, Postmark or any SMTP server.

We integrate deeply with each of these providers to handle bounces, webhooks, delivery errors, callbacks and all of that fancy stuff so you don't have to.


Fully automated bounce handling, with a dynamic retry mechanism that works.

Bounce handling is typically a hard problem requiring manual intervention and support followups. But if you have to wait for your team to deal with a mistaken bounce, you could lose a customer.

Flute's Unbouncer is a fully automated solution for safely handling bounces. We catch and retry bounces across a different provider and domain, to circumvent temporary IP/domain blacklist issues. Our bounce handling is constantly improving with an ever-growing set of data about how different ISPs and email servers behave.

As an independent multi-provider API, we can afford to retry bounces across different providers and domains without hurting anyone's reputation. Your typical email provider cannot do this, due to worries about hurting their shared pool reputations.

Smart Failover

Running an ESP is hard. API errors, downtime, and congestion delays happen. Which is why you need to use an independent API.

Smart Failover is a unique feature which you won't find anywhere else. We monitor provider-specific status issues, congestion delays, and downtime, and dynamically reroute your email through alternate providers configured on your dashboard.

Smart Failover also supports load-balancing requests across multiple providers for boosting capacity, supporting redundancy, and A/B testing your providers' performance.

Email Search Engine

Quickly find any email that was sent or received through any of your APIs.

We are the first (and only) email API to offer full-text-body searchable logs. We understand the importance of being able to follow-up on your customers, and maintain independent logs for auditing, debugging and compliance.

We even store attachments, and provide direct API access for extracting, analyzing, and exporting data.

REST & SMTP Interface

The last email API you'll integrate. Super-easy drop-in replacement.

Send email via our simple REST API, from any programming language or software.

We also support SMTP access, so you can just drop-in credentials to any SMTP library or application.

Easy Segmentation

Tired of problems managing and unsubscribing from different types of email? Flute makes it easy to isolate your marketing, transactional, and critical/personal emails.

If you don't segment, we strongly recommend it. Because segmentation makes it so much easier to manage a good email program. And your marketing email reputation with potential spam complaints should not affect your critical email deliverability.

With Flute you can even send different types of email through different providers. You might want to send critical emails through Postmark and marketing through SendGrid, for example.

Dynamic FROM

Your email FROM is probably the single most important factor in deliverability and reputation. At Flute, your FROM is configurable from the dashboard - no code editing required.

Test and measure sending from different providers or domains to compare performance and deliverability, without needing to write a single line of code.

Kibana Analytics

Flute comes built-in with access to pre-configured Kibana dashboards, the world's most popular open-source log analytics platform.

We aggregate and simplify the vast myriad of complicated events (bounces, errors, opens, etc.) from multiple providers into one simple data point: SUCCESS or FAIL.

How It Works

Flute sits between you and your email API provider(s).

  1. Signup and add your provider API keys
  2. Configure your "Virtual Flutes" to segment different types of email
  3. Start sending through our API

And then sit back and relax, while our store-and-forward queues take care of your email routing, bounces, and content storage.

Critical Emails


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Transactional Emails


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Promotional Emails



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Flute makes it easy to follow industry best-practices for boosting deliverability. Now it's trivial to do segmentation, good bounce handling and reputation management.

  • The Flute Deliverability Guarantee: If you don't see a significant improvement in your overall open/click rate after integrating Flute, we'll refund your money, no questions asked. Read more.

Delivery optimization tech developed at the University of Toronto. Read the first whitepaper.

Ready to optimize your delivery? Hook up your provider in minutes.

Drop-in dashboard for your provider.