You may be able to somewhat automatically use an email app
such as Thunderbird to get a duplicate of your GMail to your
computer; or use an iMap or POP setup (as discussed else-
where, online, when addressing actual archiving of Gmail to
a computer or at least a non-google server archive.)
{Since I don't use an email app nor do I use the ISP's provided
email account system, but have used a few free web mail sites
before Gmail from Google; I now solely use Gmail, and could
use an easier method, too, of archiving direct to the computer.
But I do not want to set up an email client software to do this.}
The ease, if it existed, of being able to have Gmail create a
downloadable .zip archive of email in dated batches, could
save a bit of time. Of course, having to open and read through
them to find a single important email's content takes away time.
There are a few ideas online about how to archive and access
Gmail, to a computer's hard disk drive or similar archive; but
one that looked somewhat promising has not made the transition
to Mac OS X in a handy GUI form: "Gmail Backup."
You could use the Gmail "archive" system in your Gmail account
and that would keep those mail items apart from your recent stuff.
Or, send those emails to a second gmail account. That would only
give you the dates they were forwarded and not a "by date" filing
system; so making copies that way makes a new kind of job of it.
• "How do I backup my GMail?"
http://ask-leo.com/howdo_i_backup_mygmail.html
Perhaps someone has a better idea in some shareware tool or
an easier path to set up a POP or other account and use a second
app such as Thunderbird to handle or make actual offline archives.
Good luck & happy computing! 🙂