I understand your disappointment, and I thank you for being a donor; users such as you are the backbone of Thunderbird. However, we are just users such as yourself, neither developers or employees, but giving of our free time to assist others. If I may offer a suggestion: when posting a problem, the more information you share in post increases the likelihood of a response. For example, knowing POP or IMAP, whether thunderbird was just updated, release version of thunderbird, plus any error messages. Knowing that, a volunteer may be more apt to respond, as the volunteer may have ideas for a possible solution. If you still do not have the ability to send messages, is that because the Send button is missing, or the 'new message' button is missing? If it is the 'new message' button, click view>folders and tick 'folder pane header' to restore it. If the 'send' button is missing from compose window, let me know and I'll provide further info. Thank you.

Thanks for the explanation. However, there is surely a controlling person or original programmer that carries out daily maintenance and improvements such as those recently implemented, it can't all function in a 'self-driving' manner? Where does my contribution go?

Your contribution reinforces problems that have already been reported and are under investigation. The Thunderbird support structure is huge and most bugs are intertwined such that a problem reported on the forum here is not such that it can be quickly assessed and repaired and updated in a day or two. Thunderbird does not have daily maintenance, but code changes go through multiple levels, often taking weeks for what seems a simple change to get from coding to a release version. I assure you that a senior manager reviews activity here and summarizes within the development team regularly. Thank you for caring and for continuing to provide feedback and report problems as they occur.