Email thread replies are typically arranged in chronological order starting from the first reply to the most recent one. This arrangement is helpful for recipients who are following the conversation because it's organized the discussion in a simple structure.
How are emails threaded?
An algorithm compares and matches segments, grouping emails and attachments from the same conversation—known as a thread group—together into a neat thread. Next, the technology analyzes the text, sent time, attachments (and their text), and the sender of each email to determine uniqueness or inclusiveness.