Emails within a PST folder are stored in a sequential list and so there is some inherent order, but this order normally just reflects the order that items were added to a particular folder and it is not necessarily date-ordered. In general, the order will be roughly the received or created date order, with older items appearing first and new items being appended to the end. However, if you were to take some old emails and move them to a different folder, for example using Outlook, then those old items will also just be appended to the end of that folder, instead of shuffling everything around to re-sort them.
When GoldFynch extracts emails from a PST folder, it prepends a 6-digit number to the file name, which corresponds to this stored ordering within that PST folder.
Therefore, in new productions you create through GoldFynch, if you select the "Alphabetically by folder & file name" option in Step 5 of production (Sort Order), the emails within a particular PST folder will be grouped together, and in the same order they are stored within the original PST folder (due to the prefixed number that gets added).
NOTE: The sort method in productions created in GoldFynch only affects top-level emails/families. Any attachments will always immediately follow their parent document in the Bates sequence, regardless of the selected sort order.