Outlook has this feature for decades. I figured by now Thunderbird would have the same.
The idea/feature: When you sort an email folder, by Date, by Correspondent, by Subject, etc., ascending or descending, in Outlook (and other email clients) all one must do to index down to the first character of the field, is to simply press that first character on the keyboard, and client moves down to the first occurrence of that character. Very handy to jump down the column to a specific character. Maybe there is some similar feature in Thunderbird, but I'm not aware of it.
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