Is it possible to restore permanently deleted messages in Gmail?
Yes, as an administrator you can restore the user’s data from the Admin console.
A message is permanently deleted when the user’s trash is emptied. You can only restore data that was deleted within the past 25 days, after that it’s gone forever. To make it easier you can specify a date range (in the past 25 days) to restore the messages that were deleted within that range. You can do it the same way for Drive data.
It might be helpful to read the G Suite Support article about this topic.
To find more information about G Suite in general click here.