Messaging Server provides full support for hosted domains—email domains that are outsourced by an ISP. That is, the ISP provides email domain hosting for an organization by operating and maintaining the email services for that organization remotely. A hosted domain can share the same Messaging Server host with other hosted domains. In earlier LDAP-based email systems, a domain was supported by one or more email server hosts. With Messaging Server, many domains can be hosted on a single server. For each hosted domain, there is an LDAP entry that points to the user and group container for the domain and provides various domain-specific default settings.
When you define a domain, there must be a corresponding domain entry in the directory; that is, you must have an LDAP entry for the domain. Attributes such as mailAlternateAddress and mailEquivalentAddress depend on the existence of domain entries in the directory. Contrast this with vanity domains, which are domain names associated with an individual user, not with a specific server or hosted domain. The vanity domain does not have an LDAP entry for the domain name.
Because of their increased operational overhead, vanity domains are not recommended.