Upon a new install of Eset Smart Security a couple weeks ago, suddenly Thunderbird comes up with the following message: ALERT - The current command did not succeed. The mail server responded: Message contains invalid header This happens when first launching Thunderbird in the morning, once for each new message. Then it happens again when OPENING the message. I suspect the following issue is the underlying problem, and I think ESET might be causing the header to get corrupted. But that's as much as I've been able to surmise. http://kb.mozillazine.org/Message_contains_invalid_header I'm running the most recent versions of Thunderbird (22.214.171.124) and ESS (4.0.314.0) on Windows XP SP3 (all critical updates installed). I have the following TB add-ons installed: Lightning, Provider for Google Calendar, and Zindus. Is ESS truly the cause of the problem? Any solution in sight?