Thunderbird uses your system clock. I would check your time zone settings again.

Windows time zone, date, & time are set correctly!

I am wondering even if windows time, time zone, date & time, were not correctly set, wouldn't it show the incorrect windows settings?

It seems that if it went by windows time, shouldn't it be the same as shown on my lower right task bar?

Just because the clock says the correct time, it does not mean the time zone is correct.

I have seen the question numerous times and when it is off by even hours it is always a time zone setting.

I too have this problem, but time difference have shifted (more often lagging than not). I've written it off though, initially at least, as something related to me running Thunderbird through Tor (and, for clarification, it's not a time zone issue in my case, unless Windows propensity for ignoring settings and preferences is at play, again). So if you're not running it through Tor, or someone else can poke me with some insight (in my state of bliss), I'd appreciate it.

(Win 7,sp1, Thunderbird/FifoxESR v 32.1.0. +/- Torbirdy (both settings faulty) and Tor 4.0 - current lag 3h.)