This question is regarding the use of Thunderbird (or other IMAP clients) and suggested backup and encryption tools, not Gmail.
I have Thunderbird setup to access an email account via IMAP (in this case the email account is gmail). I would like to create encrypted backups of the email, perhaps by year, e.g. 2005, 2006, etc.
What are some of the ways to accomplish this? What would work best and would be most accessible in the future? Are backups by year the best way to segment the data (if necessary?)
Although my main machine is Windows 7 64 bit, I see this as a "one-off" task, meaning I'll do it once a year or so and backup 12 months worth of email at a time. So I'm not limited in what hardware/software I use to do it, i.e. I can boot up OS X or Linux to accomplish this.