On 11./12.04.2026 the chat conversations will be migrated from the chat service Mattermost to the Chat service Nextcloud Talk. Below, you will find an overview of the migration process and all further details regarding the transition.

Migration Status

• All teams and channels have been fully migrated to Nextcloud Talk.
• The migration of direct messages (1:1 and 1:n) is largely complete but not yet fully finalized and is still ongoind (as of 14.04. 09:30).
• The address chat.desy.de will point to Mattermost until 16.04.2026, which will be in read-only mode after the migration. After 16.04., the address will point to Nextcloud Talk, and Mattermost will no longer be accessible.
   

Virtual Knowledge (VK) Sessions

IT is offering the following sessions to provide a brief overview of Nextcloud Talk and address user questions (access details for the video conferences will be shared shortly below before each session):

• Thu., 09.04.2026, 09:30–10:30
• Mon., 13.04.2026, 13:30–14:30
• Tue., 14.04.2026, 10:30–11:30, VK
• Thu., 16.04.2026, 11:00–12:00
   

Preparatory measures for the migration

If you use the "Saved Messages" feature (which serves as a personal bookmark for individual messages), please forward the relevant messages to yourself to consolidate them in one place. The reason for this is that Nextcloud Talk does not have an equivalent bookmarking function for individual messages, so these "bookmarks" cannot be migrated.
 

What will (not) be migrated?

• Archived channels will be exported (i.e., backed up) but not imported into Nextcloud / Talk.
• Archived direct messages (1:1 conversations) will be migrated and will subsequently be available as archived conversations.
  Archived conversations in Mattermost can be identified in advance by the box/carton symbol before the respective name if needed.
  
  
   
• If you already had access to Nextcloud / Talk before the migration and conducted 1:1 conversations there with people you also had direct contact with in Mattermost, the contents from Mattermost and Nextcloud/Talk will be merged into the same direct message thread with that person after the migration
• Pinned messages will be visible in the chat description after the migration.
• For "Saved Messages" (a feature that acts as personal bookmarks for individual messages), there is no equivalent in Nextcloud Talk, meaning these bookmarks cannot be transferred during the migration.
   

What should be noted after migration?

• After migration, it may take a moment for the contents to load when opening a channel. Therefore, please be patient for a short while when opening a channel for the very first time in Nextcloud Talk. If needed, it may also help to select a different channel first and then return to the one in question.
• Previously, in Mattermost, there were so-called Teams within which channels could be created. Since such a hierarchical structure does not exist in Nextcloud Talk, after migration, all conversations are on the same level. The names of the migrated channels then include the team name. For example: A team called DESY with a channel Townsquare is named DESY / Townsquare after migration.

Are follow-up tasks required?

The following minor follow-up tasks may be recommended depending on your personal settings needs:

• Personal profile settings may need to be adjusted (e.g., setting a profile picture).
• Favorites need to be reconfigured.

Normally, no follow-up tasks are required. The following follow-up tasks may be necessary in special cases:

• Channels that were publicly accessible across DESY in Mattermost will be private after the migration. If the conversation should remain visible across DESY after the migration, this must be adjusted in the conversation settings after the migration. Please see here for further instructions.
• For (very few) channels that no longer have an admin, an admin will be randomly assigned. After the migration, it should be checked whether this arrangement should remain.
   

For more information on technical details and further instructions on recommended actions after the migration, click here.

What is different in Nextcloud Talk compared to Mattermost?

You can find an overview of the key changes/differences here.

Background

The coronavirus situation made a dedicated DESY-wide messaging (chat) service more important. As a result, Mattermost was initially made available temporarily starting April 15, 2020, following a decision by the DESY Directorate.

The re-evaluation in light of the expiration of the current Mattermost licenses at the end of April 2026 confirmed a continued need for a messaging service. Given the changed licensing terms and costs for Mattermost, we cannot continue using it. Therefore, after analyzing available options, we are switching to Nextcloud/Talk and integrating the messaging service into our storage cloud Sync&Share (sas.desy.de).