So, if you create a simple email message without all the Word-related baggage, does it send correctly? We generally don't approve of nor encourage pasting into Thunderbird from other editors. Apart from the inefficiency (have you ever looked at the source of an email message that has any input from Word?) it tends to be horribly unreliable and unpredictable. The only way to use Word safely, IMHO, is to use paste-without-formatting (ctrl+shift+v) but that would of course defeat much if not all of the formatting you apparently want. Anyway, let's see if you have a general sending problem, or only when Word is involved. I should add that copying to Sent is handled by your IMAP server, sending the message is handled by a separate SMTP server, and when you post from the webmail interface, yet another server is involved. So there may be a local issue with the SMTP server which would only affect a regular email client such as Thunderbird. You're using Word so why not Outlook? They are natural partners and you can probably use Word to compose your emails then send them from Outlook without any copy-and-pasting.