I have about 15 YEARS' worth of saved emails in IMAP folders. I need to MONKEY around with the structure a bit, so I wanted to do a full backup first.

Trouble is, the Google likes to offer Linux solutions which is a nonstarter for me.

If I back up my Outlook OST file.... That's all I need, really, right?

rjbinney, learn about Linux.  Either Linux or Unix are most often used on Internet servers. And the e-mail systems are BASED on the legacy of Unix in computer communications.
Thee are no lack of tutorials.
Try this:
Google: how to manage IMAP in Linux
And find loss of help. Like:
http://www.tldp.org/LDP/LG/issue35/jao.html
IMAP on Linux: A Practical Guide
OR
http://cnedelcu.blogspot.com/2014/01/how-to-set-up-simple-mail-server-debian-linux.html
How to set up a simple mail server on Debian in 5 easy steps
AND:
http://www.yolinux.com/TUTORIALS/LinuxTutorialMailRetrieval.html
Linux Mail Retrieval software

If the e-mail is on the server, and if the server runs Linux,  the format is not part of any Microsoft secret  protocol.




Thanks... Taking that on just to make sure I have a clean copy of my email structure seems like overkill.

Thanks though.Has Google tole you how much space your e-mails takes?

Here is some info about how to reduce bloat in your e-mail
https://support.mozilla.org/en-US/kb/avoiding-quota-limits-mail-servers


It's AOL, so it's virtually unlimited. I just want to make sure if my re-structuring folders faffs up the system, I don't lose anything.OK. It is AOL. 

Let's say you GOT 25 e-mails every weekday.
Le's say the average size is about 2000 bytes of text.

That would be some 260 kilo byes in a week. Let's say some attachments would be included, so double that and you have about 500 kilo byes a week.
Estimate about 50 weeks in a work year, then for the pat 15 years you would have some 750 weeks of mail, each week half a megabyte.

So you might have 325 megabytes. If it is mostly just text.

You should be able  to  download that into a local folder on any modern PC with decent hard drive space.  Might be fun.

Recently a political person made some jokes about managing a large e-mail account. Might be of some help.
http://abcnews.go.com/Politics/hillary-clinton-jokes-wiping-email-server-cloth/story?id=33165517