The license must be activated inside your installed eM Client program, not on our website nor through email messages.

In the main program window find the Menu button in the top left.

Open the Menu > Help >License section.

Click the Activate button, insert your key and confirm.

If there is no Activate button and this section already seems to include some License information it means there already is a license activated on this computer. If it's the correct license, you don't need to do anything.

If you wish to activate a different license simply click Deactivate first to remove the current license. The same button will then be replaced by Activate option and you can proceed using the steps above.