How about you start with some current accurate information. That way someone might be able to figure out what is happening in your instance. Thunderbird saves mail to the accounts designated sent folder by default. I have seen the odd instance where that goes wrong where the Thunderbird software and the server software are using different languages. But it is not a general issue. Who is the mail provider? Is the mail account IMAP, POP or EWS? Is your account configured to actually save sent email in account settings > Copies and folder? See below for some of the settings options. <img src=https://assets-prod.sumo.prod.webservices.mozgcp.net/media/uploads/images/2025-11-08-21-39-27-88cc4e.png> Just a point of interest, I see you flag this topic as having something to do with Android, despite posting in the desktop forum. Is it Android? That is a completely different product that happens to share a name. The source code is not even on the same servers.