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Jira Server & Jira Data Center
You have to purchase a license that matches the license of your Jira system in terms of users.
For every new release of our Outlook add-in there will be a new version of the related Jira App.
The Jira app has to have the same or a newer version than the Outlook add-in.
If the Outlook add-in is newer, the user gets a notification message that tells him to update the related Jira app.
If the Outlook add-In is older, the add-in will just work as before due to backward compatibility.
In case of a license error the user will be notified. The error will also be visible in the app management in the Jira administration.
Example
Jira App Version: 24.1.1 0 → Outlook Add-in version: Any version up to version 24.1.1 0 will work.
Jira App Version: 24.2.0 → Outlook Add-in version: Any version up to version 24.2.0 will work.
Jira Cloud
You always have the newest version of the Jira app installed. Atlassian cares about the updates.
As Atlassian handles the versioning of the App automatically, the version of the Jira Cloud App can be ignored and does not tell something about the "up-to-dateness". Changes of the App in the backend does do not result into a new version in most many cases.
The version of the Outlook add-in is independent from the Jira app version. Any version of the Outlook add-in will work with Jira Cloud from the license perspective, as long as the related Jira Cloud App is installed.
Example:
Jira App version: 2.0.2-AC → Any Outlook Add-in version will work (Atlassian will update to e.g. 2.0.3-AC automatically, if available).
Jira App version: 2.0.3-AC → Any Outlook Add-in version will work.