Genius Thunderbird plugin that sets a custom From address based on the recipient address of the email. Genius, exactly what I've been seeking for years. Now to get it setup...
A somewhat useful open database of company data worldwide. Supports crude search and returns data in json. Essentially Companies House data in the UK, so not ultra useful.
A custom "from" plugin for roundcube that auto sets the from address to whatever email address the message was delivered to. Mind blowingly awesome.