EmailEngine Email API

Access any email account to receive and send emails using an easy-to-use REST API.

With EmailEngine, you can focus on building features that matter instead of spending time rolling custom IMAP and SMTP connectivity logic.

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Get EmailEngine for your system


EmailEngine is a self-hosted application that opens a permanent IMAP connection against every registered email account to translate API requests to IMAP commands and monitor changes on these accounts. EmailEngine uses Redis as its data store, so you have to have Redis installed for EmailEngine to work.

This example assumes that Redis is installed locally and does not require any authentication; see the configuration docs for other options.
You can find Platform-specific instructions for installing Redis and EmailEngine here.

  1. Download and install EmailEngine
  2. Run EmailEngine from the command line
$ emailengine
  1. Open in your browser
  2. Next, generate an access token and use it on the API Reference page to try out some API calls

EmailEngine does not require any special privileges besides potential firewall exceptions for ports it is listening on.

Alternative to rolling your own

EmailEngine is an excellent choice if you consider building IMAP and SMTP integration for your service in-house and are not interested in the subtle details of a boatload of RFC specs. EmailEngine is like an email class library but on steroids.

Using an IMAP library only takes you so far; anything more complex than listing the current mailbox state and you're on your own.

Full control
Own the stack
Complexity hidden away

Easy to use REST API

The REST API with JSON payloads you expect it to be. No need to know IMAP internals, weird encodings, or juggle with different IMAP extensions.

Unicode strings
Binary attachments
Paged listings

Webhooks support

EmailEngine sends you a webhook any time something happens on the user's email account.

Incoming emails
Deleted emails
Message flag changes

Almost perfect deliverability

EmailEngine sends emails through the user's email servers, so for the recipient, it seems that the email came from the user directly and not via some third-party sending service.

Uploads to Sent Mail
Adds reference headers
Flags answered emails
Bounced email detection

Fluent OAuth2

EmailEngine can speak OAuth2 fluently with Gmail and Outlook servers. You can also choose to manage token renewals yourself, or you can let EmailEngine handle everything.

Hosted authentication

Redirect your users to EmailEngine's hosted authentication form, and once the email account is authorized, the user is sent back to your app.

You can still use API calls to register accounts without redirecting users to EmailEngine's UI; hosted authentication makes the process slightly easier to set up while developing.


Look under the hood

Multiple logging options, including full IMAP transactions for debugging.

Full transaction logs
Per-user logs


Who is it for?

Anyone who wants to integrate their system with existing email accounts. For example a help desk service that runs on top of support@domain.tld account and converts incoming emails to support tickets.

How does it work?

EmailEngine keeps an open IMAP connection against every registered email account and listens to changes on these accounts. Also, whenever you request some action over the API, EmailEngine "translates" that request into an IMAP command.

Do I need a license key?

You can try out EmailEngine without a valid license key as long as you wish and only buy one once you see that EmailEngine works for you.

Beware, though, that EmailEngine stops syncing all accounts after 15 minutes of run time if the license key is not set. You would have to restart the app or provide a valid license key to enable syncing again.

Do I need to pay for multiple licence keys?

In general, no. You would pay not for EmailEngine, the software, but Postal Systems' yearly subscription. If your subscription is valid, you can generate as many license keys as you wish without any additional cost.

What are the requirements?

EmailEngine uses Redis as the caching database. That's about it. If you have any decently recent version of Redis installed, then you are good to go. Ensure to keep the latency between Redis and EmailEngine as low as possible to improve the performance.

Which kind of protocols are supported?

EmailEngine uses IMAP to access mailboxes and SMTP to send out emails. Alternative protocols like POP3, ActiveSync, or the Exchange Web Services (EWS) SOAP API are not supported but might be in the future.

What about data compliance?

EmailEngine is self-hosted and not an external service, so it does not send or store data outside your network. It only keeps minimal metadata required for syncing and caches but not the actual contents of the emails.

Can I run multiple EmailEngine instances that share the same Redis database?

At this point, unfortunately, no. Horizontal scaling is on the roadmap but without an ETA.

I'm getting a lot of 504 errors for API calls

IMAP is a single-threaded protocol which means that you can only run a single command at a time per account and have to wait until it finishes before you can issue another command. So if you make multiple API requests against a single account at the same time then EmailEngine queues these requests and processes these in order, one command at a time, while other queued commands will wait their turn. If a queued command can not be processed in 10 seconds, then EmailEngine aborts it with the 504 response.

You have two choices, either do not send multiple requests at the same time or increase that 10-second limitation. Look for the "Max command duration" option in the configuration options documented here.