>Year end tasks here include moving 2Y old mails into "old" folders, which grow once a year and are somewhat hefty in size. Then they are saved right away, so that for the next 12 months the newly arrived mails are in smaller folder/files (13 months worth in Jan, 24 in Dec) which can be backupped faster. Searching still easy if you organize the folder structure to easily drill down.

My work related email is in the inbox of the work related email account, and each year thereof is in a separate subfolder. In a few days from now, ctrl+a on the list, create new folder with 2013 in the name, paste, compact inbox, done. All indexed and searchable.