I'm running Thunderbird 11.0.1 under Linux Mint 12 for all my email addresses (all IMAP). I have recently found that when I reply to an email it only includes the recipient's email address in the reply on a random basis. More often than not, I have to add them in each time. If it did it all the time I would think it was a setting but random being random, I can't pin this one down. I have reinstalled without any change. Any ideas?