The setting to 'empty Trash on exit' is account specific. Have you set up each mail account/email address to have those settings?

YES EACH MAIL ACCOUNT IS SET TO EMPTY TRASH ON EXIT I thought it was clear : ONLY BY ACTIVE ACCOUNT IS TRASH EMPTIED By active account I mean the last account I had read on, not the others And again YES by each account is "EMPTY TRASH ON EXIT" is set. AND AGAIN ONLY ONE TRASH IS EMPTIED. I think some one can not or will not understand what is writed.

Do not use capitals as it implies you are shouting and is against this forums etiquette rules. Do not be rude, it does you no favours. If I ask a question to clarify a point then please simply respond with information in a civil manner. You would be amazed how many people will fail to check all the settings are correct for all accounts and I do not assume your technical know how.

Are all the accounts set up as Imap? Or is this effecting some Pop and some Imap ?

If Imap, are all imap accounts also set to 'Clean up (Expunge) Inbox on exit' ? Do you compact all your folders in all accounts on a regular basis?

For each account....Message storage type: Are you using Maildir or File per folder (mbox) ? Are all mail account using the same message storage type ?

Restart Thunderbird in safe mode, make sure an email is in each mail account trash folder. Then exit and restart in safe mode. https://support.mozilla.org/en-US/kb/safe-mode-thunderbird#w_how-to-start-thunderbird-in-safe-mode Please report back on results. Did all accounts empty trash ?