So I followed all the Postfix steps found here to get PF up and running on my Linode. I can send email no problem, but I'm unable to receive it! Instead the email bounces back with this error:

Message from yahoo.com.
Unable to deliver message to the following address(es).

<milo@limecat.org>:
64.62.190.199 does not like recipient.
Remote host said: 554 <milo@limecat.org>: Recipient address rejected:
Relay access denied
Giving up on 64.62.190.199.

Can someone tell me what I need to do to fix this?

Your postfix setup does not believe that it has to do local delivery for addresses in the limecat.org domain so it tries to relay the mail and finds that this is prohibited - hence the error message.

Local delivery is controlled by the value of mydomains in /etc/postfix/main.cf. The instructions you used do not appear to set a value for mydomains so it will default to '$myhostname localhost.$mydomain'.

The instructions you followed tell you to set the hostname to server1.example.com and does not set the domainname. Postfix will then take the value of hostname, minus the first component (server1 in the example) as the domainname for the mydomain variable.

postconf | grep ^my[dh]

will get you the current values of the important configuration variables.

Working example:

root@fremont root # postconf | grep ^my[dh]
mydestination = $myhostname, localhost.$mydomain, $mydomain
mydomain = clissold.nl
myhostname = fremont.clissold.nl
root@fremont root #

I'm guessing that your mydomain is something other than limecat.org.