Thunderbird: Auto update all IMAP folders/subfolders
https://support.mozilla.org/en-US/kb/config-editor Menu Edit > Settings > General > Config Editor… Advanced Preferences mail.server.default.check_all_folders_for_new true
https://support.mozilla.org/en-US/kb/config-editor Menu Edit > Settings > General > Config Editor… Advanced Preferences mail.server.default.check_all_folders_for_new true