To get assistance, you need to provide some details on this. Are you saying messages are stored sometimes and sometimes not? In one folder one day and in another a different day? Resolving this might take lots of research, so clarification is important. thank you

David, 1) Only one of our Tbird Accounts has this problem. 2) It shows two (2) "Sent" folders, one labeled "Sent" the other labeled "Sent Items". 3) It seems that actual "sent" emails do get into one, or the other, of the folders. However, as of this writing, one folder is empty, and one has a handful of actual sent emails. Our version of Tbird is, I think 146.0. Your help with this is greatly appreciated and "Happy New Year"! Charles Kindt

This ties, normally, to the email provider. That is, the email provider may default to 'sent item's, whereas thunderbird assumes sent. My personal email provider, for example, uses 'Drafts' for the drafts folder, but thunderbird uses draft. So, I have two such folders. Since these are IMAP accounts, I rightclick on account name, click properties and 'choose' and unsubscribe from one. For you, I suggest using account settings>copies&folders, and selecting one, and in the account properties, unsubscribe from the other. Where possible, I suggest setting to whatever the email provider defaults to. You can usually confirm that by logging to the online account. And I wish you safety and happiness in 2026. And no problems with thunderbird. :)

If you have two Sent folders, one is the expected /[Gmail]/Sent Mail or possibly, just /[Gmail]/Sent. The other Sent folder is in fact a "label". You can delete that label by opening GMail in a browser, go to Settings, Labels, and remove it. That label can also appear as something like [imap]/Sent. You can contact me if clarifications are needed.

What happened when you followed David’s advice?