Wanted: Delta Chat Core Developers

Hi everyone,

as you might have heard, Open-Xchange is working on a new emerging standard for messaging on top of email - we call our variant “Chat Over IMAP” or “COI” in short.

We collaborate with Delta Chat in various ways:

Now, to the actual topic of this message: we are hiring! We search for capable C and Rust developers who are willing to work fulltime on future Delta Chat Core topics. Here are the details:

The OX Engineering Team is looking for a C & Rust Developer to join the Team.

We’re looking to hire a software engineer to join the OX Engineering Team, preferably in Espoo, Finland, but applicants located elsewhere will also be considered.

Your passion / your job

You will contribute to the Open Source projects Delta Chat Core and Dovecot to establish viable, federated and open alternatives to proprietary messaging solutions. As such you will work on making the client middleware Delta Chat Core compatible to the COI (Chat Over IMAP) project. You will work in close cooperation with the Dovecot IMAP as well as the client team of OX.

  • Writing excellent quality, understandable and clean C99 and Rust code
  • Understanding Open source software – Your name will be publicly show with your commits
  • Secure coding practices
  • Writing unit tests and/or CI tests for your newly written code
  • Designing and developing new features
  • Debugging bugs, crashes and performance problems. Sometimes this requires understanding external software (or even hardware), such as the (mobile) OS, storage system, load balancer, firewall, etc.
  • Writing performance critical code.

Our ideal candidate would have the following experience and skills

  • Bachelor’s degree in Computer science or corresponding work experience

  • Excellent C language skills, since Delta Chat Core is mostly C99 code

  • Good Rust skills, as future parts of Delat Chat Core will be implemented in Rust

  • Good debugging skills to understand and fix crashes and other strange behavior (gdb, valgrind, strace)

  • Experience with C on mobile OS (NDK on Android, iOS)

  • Determining operational feasibility by evaluating requirements, analysis, solution development, and proposed solutions

  • Ability to work independently with support the of the OX team

  • Goal-oriented working style and high self-motivation

  • Team player and ability to communicate well amongst peers

What do we offer

  • Working on modern software in an international team
  • Wide scope to develop your own ideas and projects
  • Possibility occasionally to work from home and the opportunity to work from one of our well-appointed worldwide offices
  • The most current and jazzy equipment
  • Continuous personal development & training
  • Flat hierarchies combined with an "Open Door" policy
  • Great fringe benefits

About Open-Xchange

Open-Xchange (OX) is a market leader in Mail / Messaging and DNS-based security services, with more than 200m seats sold through international hosting and telco providers worldwide, including partners such as 1&1, Orange, Italiaonline, Comcast, GoDaddy or Softbank.

We at OX have our roots in Open Source, and this has shaped our view of the world and culture – open, diverse, and with a bias to act, giving everyone at OX room to take responsibility within their team and grow. OX believes in an internet that is open, safe and free. We want to create competitive products that allow our providers to deliver secure internet services with a great user experience, and that respect privacy and generate value.

With some 270+ people worldwide, OX develops and operates Open Source software (aaS) for mail / messaging and collaboration / productivity. OX’s Dovecot is the world’s dominant open-source IMAP server software, and our PowerDNS provides secure DNS services to our telco customers and their users.

Our business is fast-paced and changing constantly. We are looking for people who share our beliefs, who are out there to make a difference, are entrepreneurial and enjoy working in a high-tech environment as part of a truly international team. OX is headquartered in Cologne, Germany, with further locations throughout Germany (Hamburg, Bremen, Dortmund, Cologne, Olpe and Nuremberg), the USA (Louisville, KY), Finland, the Netherlands, Italy, France, Spain and Japan (Tokyo).

You will mostly work on our product Dovecot, which is an open source email server software for Linux/UNIX systems. Most of the Dovecot Engineering team works from the OX office in Leppävaara, Espoo.

Recently OX has also started developing COI (Chat Over IMAP), which is a new chat solution based on email. COI differs from most other chat systems in that it is fully federated, so anyone can develop and run their own clients and servers for it. And because it’s based on email, you can immediately chat with anyone who has an email address!

If you are interested, please contact Jochen F. Schude for further information - or send us your paperless application with a cover letter including your CV, certificates, salary expectations and the earliest possible date of entry by e-mail to recruiting at open-xchange dot com.

If you have any questions or feedback, please let me know!

Many thanks in advance,




You will find our current specification draft here:

Note that server side specs will follow, as we plan to extend IMAP and SMTP for easing messaging over email.

Generally, you will find more information at https://coi-dev.org and you can subscribe the COI developer mailing list by sending a mail to dev-join@coi-dev.org.

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