I was asked by a client where Exchange 2003 Relay Restrictions are stored? The SMTP Virtual Server in Exchange 2003 is actually apart of IIS and as a result its configuration is not stored in Active Directory (for the most part). This means if you recover an Exchange 2003 server using the Disaster Recovery switch you will need to re-enter this configuration.
See Recovering a failed Exchange 2003 server:
The relay restrictions are stored under a series of REG_DWORD and REG_MULTI_SZ values under the following registry key:
For more information please see the following Microsoft KB article: