Since version 5.0, there is a "Suppress hidden elements of documents" option under Internet Options->Email, which controls what to do with hidden stuff of documents when sending it in Emails [1].

The problem is, that this option is on the page that is totally hidden on Windows, so Windows users are unable to control this. The hiding of the page happens historically, because when there was only the option to choose mail client on that page, it made no sense to show on Windows, because we only use Simple MAPI on Windows, and never call a mailing client directly on that OS.

However, the new option made that page make sense on Windows. So either the option should move somewhere to be available on Windows, or the page should be shown on Windows instead, and only the specific controls on it hidden conditionally.

[1] https://wiki.documentfoundation.org/ReleaseNotes/5.0#Maintaining_invisible_content_in_Emails