When an AppRiver spam filtering account is initially set up, it will by default be in Open mode. This means that AppRiver will process all messages regardless of who they are addressed to if a domain's MX records are pointed to a client using an active Email Security account with AppRiver. This setting is desirable for new accounts that want to make sure they do not miss any addresses.
Closed mode is a great option to use once a client is certain all of their addresses exist on AppRiver's server. Setting your domain to Closed mode will only process mail for the addresses entered in our database and users listed in the 'User List' will have the option to receive Held Spam Reports. Closed mode will not bounce the messages, as this would let spammers detect valid addresses, it will simply hold all incoming messages for users not listed in the web interface after they are received.
If you have Hosted Exchange, we will automatically place your domain into Closed mode/'Delete' and keep all addresses in sync for you. However, if you do not have Hosted Exchange we recommend using LDAP to keep user addresses, alias accounts, email groups or email lists in sync. Of course, it would probably not take long for the missed users to realize they are not receiving email and promptly notify you.