Sometimes it is useful to set the maximum number of issues that can be exported.
You can also do it in ImpEx.
First, click on the 
icon (1), then select the option "Add-ons" (2).
This will take you to the "Add-ons panel" where you can select ImpEx Configuration from the sidebar:
After selecting it, you can set the maximum number of issues that can be exported here:
(If you set 0, you can export as many issues as you want.)
You can also select what to happen if a user wants to export more issues than the limit:
- Warn the user, but he can export (1)
- Warn the user but it is not allowed to export (no button shown) (2)
