Novy TB ma iny typ defaultneho profilu, staci si to prepnut na stary a maily tam zase budes mat.
Podobny pripad je, ak pouzijete Mozbackup pre obnovu.
https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-thunderbird-profiles
V about.profile na svojom druhom profile zvolis default, ci si si vybral spravny si overis v Open TB in new window.