Sorry, we’re closing! On October 16th.

TL;DR: We failed at product-market fit; servers will be shut down on 2020-10-16 at 16:10 CEST; a data export function is in the works; all software will be released under an open source license.

Dear Kullo supporter,

it has been a long journey since we started Kullo in late 2012. With the idea of making secure communication accessible to everyone, we reached many milestones such as designing an end-to-end encrypted messaging protocol, launching the desktop apps in 2015, and building mobile applications. Unfortunately, we never found product-market fit. The number of paid accounts as well as the free usage of Kullo remained at a constant low level. The development of Kullo slowed down a few years ago and finally came to a halt since the project was not having enough traction to justify further investment in terms of money and development time. We have been looking into expanding our business into related fields and discussed potential collaborations with other companies, but it didn’t work out in the end. In order to avoid risking bankruptcy of Kullo GmbH, we decided to do a clean liquidation. Consequently, all services provided by Kullo GmbH will be shut down during 2020.

Kullo will be operational until the shutdown on October 16th 2020, 16:10 CEST. When the servers have been shut down, it will be impossible to download or send messages. Already downloaded messages will remain accessible, though.

We are developing an export feature which we will release at some point this spring. It will allow you to export your conversations and attachments. This export feature will only be available in the desktop apps. If you only use Kullo on your phone or tablet, you will need to install the desktop app and download your inbox before October 16th. Please note that syncing the entire inbox can take a while, depending on its size and the speed of your internet connection.

All software that we’ve developed will be available unter an open source license (BSD 3-clause), allowing you to build the Kullo client or server on your own, or just reuse some components of it.

For all shutdown-related questions, the best way to contact us is by sending an email to

This is a sad moment for everybody involved: customers, users, founders, supporters, investors, family and friends. But after carefully considering the options, the best we could do was to ensure a smooth offboarding and a controlled shutdown.

We want to say thank you to all the great people who believed in us and without whom we couldn’t have gotten this project off the ground. They helped us with advice, money and moral support. They gave us opportunities we wouldn’t have had without them. And, last but not least, they advocated for more privacy by using the product and spreading the word. Thank you!

Simon and Daniel

Recent product updates & roadmap

Kullo is in active development on all five supported platforms, taking one step at a time instead of huge yearly releases. Today we’d like to show you recent product updates you might have missed so far.

The emoji keyboard in Kullo for Desktop

emoji_keyboardExpressing our emotions in written text is getting increasingly popular. While mobile platforms usually come with full emoji support built-in, desktop systems need some extra work. To make it possible to communicate between desktop and mobile without friction, we made it possible to type in emojis in Kullo for Desktop. Open the emoji keyboard by pressing Ctrl+. (control and period) on Windows/Linux and Cmd+. on OS X.

Sync of sender information

sender_informationThe sender information (name, organization, avatar and footer) are now synced across all your devices, giving your Kullo messages the same professional appearance, no matter from where you send them.

And like everything that is synchronized in Kullo: all of your data is encrypted before being sent to your Kullo provider. So this information is only accessible to you and those who receive your Kullo messages.

Unread messages indicator on iOS

KulloUnreadMessagesNumberIos_smallKullo for iOS will now show the number of unread messages next to the app icon, giving you the confidence that you’ll never miss an important message.

Large file handling

During the latest updates, support for attachments up to 100 MB per message has been improved to be faster and more reliable on both desktop and mobile platforms.

For those who are eager to see what’s coming next, we published or roadmap board. Check it out and send us feedback:

The Android SD card directory “amfb”

2016-08-01 android sdcard amfbUp to version 33, Kullo for Android stored images captured by the phone’s camera to be used as a sender avatar in the SD card directory “amfb”. The files are called img_xyz.jpg where xyz is a long number.

This was a mistake because Android apps should usually store their data in an app specific directory. We fixed the issue in version 34.

Since “amfb” is a public directory that might be used by other apps, the files cannot be deleted automatically. Feel free to delete those files using a file explorer or by mounting the SD card on your computer.

We apologize for any inconvenience.

Using multiple Kullo accounts on Android

With the current update Kullo for Android version 29, you can switch between multiple Kullo accounts without re-entering your MasterKey. This is the next step to provide a consistent experience across all devices, on desktop and mobile.

The “Logout” button was relabelled to “Leave inbox”, indicating that no data is deleted when doing so. Push notifications are currently only sent for the inbox that is opened.

Note that right now the only way to delete an account from the device (i.e. MasterKey and plaintext messages) is to uninstall the app or clear the app data. We’re working on an account management screen that will allow you to delete single accounts.

Happy account switching!

Image by Phil (CC BY 2.0).

Going Push

With the start of our mobile apps for iOS and Android in December, we received a lot of positive feedback from our users. But there was one thing missing, which bothered most of you: push notifications.

2016-02-05 pushWe’re happy to announce that with the recent mobile updates Kullo has push.

This makes Kullo not only a secure and user-friendly communication channel, but a reliable one as well. With push notifications, you see incoming Kullo messages right away and with push on the other end, you know that your Kullo messages will be read in time.

When you open the app by clicking on a notification, a sync is triggered automatically, which eliminates the need for manual syncing. Kullo for iOS version 18 and Kullo for Android version 27 are available on the AppStore and Google Play today. To enable this feature, we had to add some additional permissions in the Android app, so you will be asked to grant additional permissions.

„Mails ohne Mitleser“ – Kullo im Interview auf Kiez.FM

Anfang Dezember war Kullo-Mitgründer Simon Warta zum Interview beim Berliner Radiosender Kiez.FM eingeladen und wurde unter dem Titel „Mails ohne Mitleser“ von Moderator Adrian Garcia zum Thema Produkt und Unternehmen ausgefragt. Viel Spaß beim reinhören:[…]/mails-ohne-mitleser/ (Podcast, 16:24 Minuten)

Image by Patrick Breitenbach (CC BY 2.0).

Choose your update speed

At Kullo we follow the principles of agile software development, which means having short development cycles, continuously test every change in code and been able to release fully functional software at any given time. That allows us to quickly respond to user feedback (e.g. fixing bugs or usability flaws) and release security fixes within hours.

We don’t differentiate between bugfix releases and feature releases. In fact most releases contain a bit of both. Thus there is always one current version of Kullo only and no confusion about which version to choose.

While been able to release quickly has it’s advantages, there are drawbacks too. Most of all we don’t want to annoy our users with too many update processes, which always take a minute or two. Continue reading