Skip navigation links


Chat Over IMAP (COI) the universal chat protocol


Get started

COI is a universal chat protocol that is Free, Open, Easy and Safe.
Developers are not required to build or maintain a server and can reach 7 billion active accounts (with 3.8 billion unique users).










COI is a free & open standard built on top of the IMAP and SMTP standards. The COI ecosystem is made up of the COI Standard plus the compatible Client Apps and Email Servers. COI works with all email servers, but IMAP servers can be enhanced with extra COI capabilities. These extra capabilities make the development of both services and applications much easier and more powerful.



Email is the most ubiquitous messaging system in the world with far more active users than any other competing messaging service (7 billion accounts from around 3.8 billion active users).

Email is open & free: anyone can use it and implement messaging apps and services for it.

Email is federated & permission-less: you can plug in your email services and don’t need to ask anyone for permission. You can even host your own private email servers.

Email is trustable: choose your preferred provider and app freely, don’t be restricted to one single provider and solution.



COI consists of a client-side standard and a server-side standard. As a developer, you can create apps, bots or any other services based on these standards – using the programming language, OS and environment of your choice.

OX COI Messenger Beta

This short video shows how email can look by using the new OX COI Messenger. The video takes you through all the main features and introduces you to the new face of email.

Introducing COI

This bootleg video was taken at the Open-Xchange Summit in Madrid where CEO Rafael Laguna and PM Robert Virkus explain how COI was taken from conception to Beta.


Sign up to the COI developer mailing list by sending a mail to or contact us by writing to

Sign up


COI is the only ecosystem that provides openness, a strong messaging basis AND overcomes the network effect.

With its built-in backward compatibility, you can reach any email user in the world. This means COI can already connect 7 billion active accounts (with 3.8 billion unique users).

No server required: COI works with any email server and even better with a COI – enabled email server – this means that you don’t need to build and maintain your own messaging server.

Interoperability with other apps: thanks to our specifications (and a future optional compliance program), COI apps will be interoperable.

Great library support: no matter what your preferred language, there are many IMAP and SMTP libraries available.

Start building your COI
Application today

Get started