press WindowsKey+X and select CommandPrompt from the menu

Type ECHO %TZ% and press enter. Did you get information or simply a repeat of the %TZ% on the new line

Did as suggested, response was %TZ%

well that rules out a rouge environment variable.

Have you checked your systems timezone information and date formats?

Thunderbird contains no information at all with regard to this stuff. it is detected from the system settings. The exception being calendar stuff which has setting on options. But you do not mention calendar dates.

Hi Matt According to Win 10 Settings - Short date format: d/MM/yyyy Long date format: dddd, d MMMM yyyy Time zone: (UTC +12) Auckland, Wellington Country: New Zealand System is displaying correct date format in Win Explorer, Win Settings and on the task bar but not in Thunderbird Don't have the TB calendar installed Thanks

As a Linux user, I found that some voodoo was needed to set a date/time format that Thunderbird could use. When I switched to a different distro recently the trick I knew stopped working.

I used the Super Date Format addon to manage the date format in Thunderbird. While in your case I suspect there is a"proper" way to fix it, this addon might be an acceptable workaround for you.

Hi Zenos

Have tried the suggested add on, it only changes the date format in the date column but not on the message header.

Thanks all the same for your suggestion

D