re:''Email Source starts with "From - {date}".'' That is normal in a Thunderbird folder although some imap accounts folders may look different. It takes the format of day, date, time, year and does not mention timezone. It may also be a bit later in time than in the 'Date' header if there is a small difference between sent and downloaded. the 'From' date is when downloaded: eg: From - Wed Jul 28 14:57:18 2021 the 'Date:' info is when email was sent. eg: Date: Wed, 28 Jul 2021 14:56:11 +0100 You may also notice the format for Date: is Date: {date time timezone} which ends with time data plus any adjustment for different time zones. re : ''but some emails seem to be really sent out with that line there.'' The line is there in your copy. Even if you sent from one email address and then waited a few moments and used reply, but you did not use 'Get Messages' - you allowed Thunderbird use the check server every x minutes. You would see nothing is the same because it is a unique new email sent and received/downloaded at a different time. Replies do not contain headers of original email. 'Forwards' may contain full headers if that setting has been set here: Menu app icon > View > Headers but the first From will say eg: From: 48 2021 <> , so it has been abbreviated. The real 'From:' header data is not located before all the server received etc data. Ideally, you should not be ending any headers as the original sender to you may not appreciate you forwarding personal data to potentially unknown persons. re: ''Does the word From cause any trouble due to similarity with the top "From:" header?'' No. There is no way any email can get sent where the 'From' data is not an email address, so clearly it has no effect on the 'From:' email address header. Basically, do not worry, nothing is wrong. Advise you never forward headers as they contain personal data. Although it may be required within an organisation as an internal requirement.