Masking an email address

I was wondering if it’s possible to ‘mask’ an email address with Exchange 2000 sp3.

I use the term ‘mask’ loosely here, because I don’t know how else to describe it.

I have a domain registered with the zone ‘mydomain.com’ and it’s hosted on a public site, zoneedit.com.

I have an internal domain with the zone ‘corp.mydomain.com’ on my network, and my exchange server is running in that domain.

What I want to do is when I send email, it will show my email address as ‘someone@.mydomain.com’ instead of ‘someone@corp.mydomain.com’.

Also, when someone sends an email to ‘someone@mydomain.com’, it will forward it to ‘someone@corp.mydomain.com’.

Is this possible? How should I configure exchange? Any configuration in DNS as well?