how to send libre office doc to email
The best choice is the Thuderbird email client. It is a multiplatform software. Just download, install it (set is as default email client), set the mail accounts, and use it.
Do it you with your usual mailer program as an attached file. This is much safer and reliable than trying to connect LibreOffice to you mailer daemon. Note that you can’t connect to webmail applications (the mail interface using an internet browser) because they have no mailer.
You didn’t mention your OS name (nor LO version), so answer can’t be more precise.
If words like “mailer”, “daemon”, “webmail”, … don’t ring bells for you, don’t try to interface LO with an SMTP daemon. This is a technical task requiring installation of various software bricks with the risk of damaging your system if you make a mistake.