Справка LibreOffice 7.5
On the Mail page in the Hyperlink dialog you can edit hyperlinks for email addresses.
Assigns the specified email address to the hyperlink. Clicking the new hyperlink in the document will open a new message document, addressed to the receiver specified in the Recipient field.
Hides or shows the data source browser. Drag the receiver's Email data field from the data source browser into the Recipient text field.
Specifies the subject that is inserted in the subject line of the new message document.