Hello ! I need to use thunderbird for very large email sending (30,000+ emails to send per day). We do very dynamic and personalized email sending, and Thunderbird is an absolutely fantastic tool for this job with all the plugins available for quick and efficient iterations on our content (thanks a lot guys!). I have total control on the SMTP Server (max number of simultaneous connections etc.), however right now the main bottleneck to the sending is that the messages are processed one after the other from the Outbox. The throughput is 1 message per second, which I think is normal for SMTP. However this has a huge impact at such a volume (sending takes a whole day). I did all the tweaks I could think of such as disabling SSL to win half a second on each SMTP transaction. Is there a hidden parameter that can be set to allow the Outbox to send more than one message at a time (either by opening multiple SMTP connections, or by doing some sort of multithreading ?