As the subject says, the Enterprise Vault Archive Explorer and Search Archives buttons are not working from OWA externally for us - on Exchange 2003 and EV 9.0.2. When clicking on the buttons, it is clear that the browser attempts to connect to the internal URL.
Other OWA functions work normally - e.g. recovering items from the vault.
Desktop policy settings that I believe are relevant:
Client connection - use proxy
External webapp url - https://webmail.ourdomain.com/EnterpriseVaultProxy
Web Application alias: evanon