This Thunderbird add-on was originally created by Geoff Lankow, but is now maintained by the Thunderbird Team.
The provider allows to upload large attachments to a WebDAV account instead of sending them by email.
https://github.com/thundernest/webdav-filelink
https://addons.thunderbird.net/addon/filelink-provider-for-webdav/
The logo is provided by http://www.webdav.org/