Yes on the small QB.
Dropbox is basically a cloud service. Any file you place in a folder in your Dropbox directory is stored "in the cloud" (which basically means another computer(s) somewhere else). The files are also stored on your local hard drive (though this can be turned off, I believe....I leave it on). The Dropbox feature most important for exchanging game turns is the ability to "share" a folder with someone else. So I can create a Dropbox folder and "invite" you to share it. If you accept, we would both have access to the folder and any files placed in the folder. So, in order to use that for game file exchanges, I (for example) would create a Dropbox folder and name it (for instance) "Wilco Vs MG". Then I would create a PBEM game in CMFB and generate turn 001. Let's call it "Wilco Vs MG 001.ema" (all CM PBEM files end in .ema). You would then take the 001 file and copy/paste it into your CMFB "Incoming Email" folder and play your turn, which will generate file 002. You then copy/paste file 002 into our Dropbox folder and so on and so forth. Clear as mud?
Now there is a third party software "app" called CM Helper that a lot of us use. What it does is automate all the copy/pasting and it also let's you know if it's your turn. In addition, it has a chat function so you can taunt, er I mean communicate with your opponents without resorting to e-mails or PMs. Now you don't have to use CM Helper, but it definitely helps once you have multiple ongoing games.
Here is an example of what I see when I double clicked on my CM Helper icon just now.
As you see I have four games going and I only have one turn waiting. CM Helper automatically copied the incoming file for Battle for Chaumont to my CMFB incoming e-mail folder. Oh, and CM Helper also tells you, via the little icons, which CM Game you are playing with which opponents. That can get confusing when playing multiple games. As you can see I'm playing, from top to bottom, CMFB, CMBS, CMBN, and CMFI.
So, if you want, I will set our game up. I'll need your e-mail address to invite you to a Dropbox folder. Which nationality would you like?