Yes that is what you see in Outlook, have you ever tried reading your emails on a phone? Most Outlook users assume that it looks like that to the recipient. What the recipient often sees is nothing of the sort. From an unreadable attachment names winmail.dat to weird ugly images composed in a font the recipient does not have, all those things does outlook produce.

Sadly Apple people and Microsoft People rarely use products not from their chosen stable. So they have no idea what others see.

As you your issue with LibreOffice, it is sending your document as an attachment. As it should. The only real way to deliver a document the way it appears in a word processor is to first convert it to PDF and send that attachment. Regardless of Microsoft's attempts to do it another way.

Thank you for your response sir. my mails are mostly text and tables. as i see the mails thus sent from outlook are preserving the formatting in thunderbird too. when i go to print document. i get the format preserved. so was looking for it. Thunderbird has the feature. do not know if i am missing something or why it is not working with me. as far as viewing in phone is concerned it is not issue. it is like any other mail. mostly desktop issue.

The expectation is that you either compose a message in the email client, using its admittedly limited (but usually sufficient) formatting capabilities, or you prepare a document elsewhere and send it as an attachment, having first established that your correspondents have the appropriate tools to work with your attached document.

You have chosen a nonstandard middle way which is fraught with possibilities for failure. LO appears to be doing something logical. It assumes that you're using Writer because you're doing something ambitious that requires a complex document structure. So it sends the document as an attachment. MSO is different in that it is engineered from the ground up to use Word as the editor for Outlook. In doing so it builds enormous messages containing the entire .dot template. Unless care is taken by the author, the content is sent using a file, the proprietary winmail.dat, that some recipients won't be able to use.

Given your maverick approach, I can only suggest that having written the document, you use ctrl+a to select all the content, ctrl+c to copy it and then ctrl+v to paste into a new Thunderbird email message. Even with doing this, I think you'll generate smaller and cleaner messages than the Word/Outlook combination delivers.