Libra Office has stopped sending to email it tells me there is no email, how do I put the email back?
LibreOffice never sends e-mails (and never has done so) on its own. It passes files to an external E-Mail program which needs to be defined in Tools → Options → Internet - E-Mail. Please check there.
@anon73440385: Well - not exactly. When performing mail merge, it uses own python script, which creates own SMTP session, with own login and all the stuff. But yes, when sending a single document, it happens as you describe; so it’s important to understand what OP is doing.