What's the deal with gMail and memory usage?

Can someone please explain to me exactly how gMail functions on the OV.

I have four separate eMail accounts but the only one that I use, or even monitor, on my OV is my gMail account. Though I've had this gMail account for several years, I almost never used it prior to getting an Android phone which, of course, required having a gMail account. The account that I primarily use is a POP3 account through my ISP. I also monitor the gMail account under Windows Live Mail, on three separate computers, but since I don't use it much about the only thing that ever shows up there is the small amount of correspondence that comes from VM.

Of course, the OV actually has two Mail app icons (eMail and gMail), but both icons open up the exact same gMail account. I'm not sure I understand that either.

I guess my real question is; What effect does this single, little used, gMail account have on the phones memory?

I know on my POP3 accounts, whenever I check my email, every single incoming email gets written to my hard drive and it stays on that drive, basically forever, until I go in and delete it. Having developed, over the years, the habit of "saving" what I deem to be "important" emails, many of these messages "never" get deleted. Since all of my computers have large hard drives (in fact, "multiple" large hard drives), this has never really been a problem.

The phone, however, is another matter.

When I open my gMail account on my OV, it opens up all the emails in my gMail account and I can scroll back in time for a long ways (perhaps all the way back to algores invention of the internet). The question is, are all of those email messages actually stored somewhere inside my phones already puny memory, or is the OV just pulling up messages that are stored on Googles servers under my gMail account? Is any of this eMail business eating up any of my phones precious memory, or is it all just there for the few minutes that I actually need to look at it and then, POOF, it magically disappears from my phone?

Inquiring minds need to know.