How does internet e-mail know where to transfer?

[Scott Wendell]

We own two mail servers; NTMail on Server1 AND Exchange Server 5.5 Rev.
3 on Server2. Currently our main NTMail Server account:
te...@wendelltextiles.com located on Server1 receives e-mail and forwards it
to te...@wt.com. The user mailbox: 'Scott Exchange' on Exchange Server2 is
configured with that e-mail address and successfully receives the mail. My
question is why does this work?
I have the Internet Mail Service 'Routing' set to 'reroute' mail sent to
wt.com to <inbound>. Our domain is wendelltextiles.com, not wt.com (we don't
own wt.com, nor do I have a DNS record for the name, when I ping it the name
on Exchange server it goes outside to some other company on the internet).

1. How does the mail forwarded from the Server1 NTMail Server know that
Exchange Server2 is the recipient for wt.com e-mail?
2. I thought e-mail couldn't be collected from POP3 accounts, how am I doing
it? Is it because I'm forwarding, rather then trying to retrieve from a
mailbox? I guess everyone could set there e-mail to be forwarded from their
POP server to their exchange server to successfully collect pop3 mail in
Exchange?