I recently spent some time in Australia where the time is 10 hours ahead of the UK. When I returned home I set the PC timezone back to UK and all appears well. Messages in my inbox and sent items have the correct timestamp. However, if I forward an email from my inbox that has a timestamp of 18 April 16:26, the embedded header appears like this: -------- Forwarded Message -------- Subject: WokinghamMay Fayre - Booking Confirmation Date: Sat, 19 Apr 2025 01:26:33 +1000 From: Alan Rouse <mayfayre@wokinghamlions.org.uk> To: spike.phillips@kingschurch.org.uk This implies that it thinks the time zone is Australia, namely UK + 10 hours (UK time is UTC + 1:00). I have checked Thunderbird settings and they appear correct, saying the ''Date and Time Formatting'' is ''Regional settings locale: English (United Kingdom)'' and ''Date Text Format'' is ''Use system timezone''