Trash and Sent messages

Is there a way I can keep messages in my "sent" and "trash" folders for longer? I often find myself wanting to look up old emails but cannot, it seems they are deleted on a certain date or once a certain quantity is reached. In addition, is there a way I can set up predictive text in the "to" field when I compose an email, so it can look up all email addresses I have previously sent to and find the address I am looking for?