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CloseDeveloper reply by Dillinger
Rated 2 out of 5 stars
I tried using Header Tools Improved to "Edit full source" to edit a received Gmail message.
The edited email was synced to Gmail web, but the date was changed to the time I edited the message, not the original received date, which makes it useless.
EDIT: "Edit Message" on Outlook desktop works fine with Gmail without changing the date on Gmail web.
Blame Gmail, not this add-on.
This add-on changes the date by one second, without that Gmail will not accept any changes.
Gmail then changes the date in the web interface to the current time, the date in Thunderbird should not change.
Unfortunately there is nothing I can do about this, sorry.
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