This problem has happened twice now, whereby I don't get alerted to new emails .ie ..a system message and the email flagged in bold. When sending a message to a different account ( I have several setup in Thunderbird), I have noticed the dock icon briefly flash with the message red pending icon, then clear without a system message alert, possibly because it is so brief. My working solution is to rebuild a new profile, with the same account settings (some POP and some IMAP)bold text, which cures the problem. Does anyone know which file(s) are being corrupted in the profile and why? Many thanks in advance.