Hugo Scheer - 2018-11-21

I am running enigmail V2.0.8 as plugin to Thunderbird 60.3.1. The computer runs on Win7Pro.
When writing a message, a toggle icon on the top bar shows a lock and "protection activated". In this mode pgp communication is fine with users running pgp. However, when using this default setting, it seems that mail users not running pgp received the message unencrypted, but also an attached file they cannot open. I told them just to ignore thos file, but this causes confusion with some of them. In at least one case a friend received an encrypted message displayed on the screen he could not read.
I can, of course, toggle to "protection inactive" whenever corrsponding openly. As most of my commnication is this way, it means to inactivate protection almost every mail. I would prefer it the ohter way around, e.g. have "inactive" as default and activate in case I need it. What do I have to change in the program settings?
Hugo Scheer