Libreoffice: do not attach document in send function

Hello,
i have a problem with my new installation of Libreoffice:
Version: 5.1.4.2
Build ID: 1:5.1.4-0ubuntu1
CPU Threads: 2; OS Version: Linux 4.4; UI Render: default;

When i choose to send a document directly using: File -> Send -> E-mail
document, Libreoffice call my mail reader (thunderbird 45.2.0), appear
the new mail in composition, in the subject field there is the name of
the file, but in attach there is anything and i have to attach it my
hand, choosing it with the button 'attach'.
There is the same problem if i choose File-> Send -> E-mail as PDF

Any idea to resolve it?

Thanks
Massimo

Hello,

i have resolved.
Thunderbird was called by Libreoffice and appeared a new mail
composition window, but it was not indicated in:
Option -> Internet -> email

Massimo