Question : Can't deliver mail from outside to newly created public folder

I am using Exchange 2003 with all the latest patches.
I created a public folder and called it webmaster.
It automatically received the address [email protected].
I gave appropriate permissions to those that need access to the public folder.
I can send e-mails to it internally.  If I try to send an e-mail to it from an outside account, it fails.
Here is what the message tracking center has to say:

Internal e-mail:
5/8/2007 10:19 AM SMTP Store Driver: Message Submitted from Store
5/8/2007 10:19 AM SMTP: Message Submitted to Advanced Queuing
5/8/2007 10:19 AM SMTP: Started Message Submission to Advanced Queue
5/8/2007 10:19 AM SMTP: Message Submitted to Categorizer
5/8/2007 10:19 AM SMTP: Message Categorized and Queued for Routing
5/8/2007 10:19 AM SMTP: Message Queued for Local Delivery
5/8/2007 10:19 AM SMTP: Message Delivered Locally to [email protected]
5/8/2007 10:19 AM SMTP Store Driver: Message Delivered Locally to Store to [email protected]

External delivery:
5/8/2007 10:04 AM SMTP: Message Submitted to Advanced Queuing
5/8/2007 10:04 AM SMTP: Started Message Submission to Advanced Queue
5/8/2007 10:04 AM SMTP: Message Submitted to Categorizer
5/8/2007 10:04 AM SMTP: Message Categorized and Queued for Routing
5/8/2007 10:04 AM SMTP: Message Queued for Local Delivery
5/8/2007 10:04 AM SMTP: Message Delivered Locally to [email protected]
5/8/2007 10:04 AM SMTP: Non-Delivered Report (NDR) Generated

Here is what the event log has to say:
Event Type:      Warning
Event Source:      MSExchangeTransport
Event Category:      NDR
Event ID:      3013
Date:            5/8/2007
Time:            10:04:52 AM
User:            N/A
Computer:      MYCOMPUTER
Description:
A non-delivery report with a status code of 5.2.1 was generated for recipient rfc822;webmaster@mydomain.com (Message-ID  <373423.95444.qm@web51103.mail.re2.yahoo.com>).  
Cause: Possible causes are 1) Local mail delivery was denied because the message size was too large 2)The recipientÆs mailbox has been disabled.    
Solution: Check access permissions for the recipientÆs mailbox as well as the message size.  If the recipientÆs mailbox has been disabled, the recipient cannot receive mail; only mail-enabled account can receive mail.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

My test is sending an e-mail from a Yahoo account that has the subject line "Test" and no body.

What is my problem and how do I fix?

Answer : Can't deliver mail from outside to newly created public folder

You need to give Anonymous users access to the public folder, did you remove tem from the permissions list by any chance?  Emails coming from external sources are unauthenticated in AD so are effectively "anonymous".  Not sure exactly what level of access they need, Contributor I'd guess!