Is Thunderbird using "sent date" instead of actual received time in "Received"?
It seems as if Thunderbird (45.2.0 Danish) uses the sent date as received date and not the actual date and time of received.
In attached image the two last columns are Received and Date. The mails are from an ip camera that sends mails with an error in the date field (as shown in the mailheader in the image) but this error ought not to have any influence of the actual time of recieving the mail (which, more or less, is show in the message body)
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The "Received" value is indeed a bit mysterious. I can understand that historically one might not want to use the computer's own time since computer clocks used not to be reliable. Now we are all accustomed to ntp synchronization by default (I remember having to download and install an ntp client to make it work at all) it's easy to take an accurate clock for granted.
If it doesn't record the local time when the incoming message is processed, you'd expect the client to parse the Received: headers and find the latest time listed, this being the one when it arrived at your incoming server.
Finally, whatever value is used, Thunderbird doesn't seem able to sort on the Received column.
Your data does strongly suggest that it's using the defective time placed into the message's Date: header, and the Jan 1970 date indicates that it wasn't able to parse the defective date/time, so is effectively using 0 as the date.