I probably wasn't clear.
The free service provides either a web based mail account OR a mail forwarding service.
Mail forwarded to your ISP can be accessed using any POP email client. You don't actually access your email at mail.com since it was sent on to your nominated email address.
In my case mail addressed to my
[email protected] address gets forwarded to the mail address assigned by whatever ISP I use. I can change my ISP as many times as I like but as long as I update the address to which my mail is forwarded, any change to the sender is transparent.
This also means that I can establish several email identities, that remain constant irrespective of my ISP, for different purposes, but collect them all from the one place ie my ISP.