Per-user aliasdetourhost is now possible through the following set of features:
aliasoptindetourhost channel keyword. This is similar in function to aliasdetourhost except detouring only occurs if the user has opted in via the following attribute. The keyword's value is a comma-separated list of potential detour hosts.
LDAP_DETOURHOST_OPTIN MTA option which specifies the name of an attribute used to opt the user in to the detour (assuming of course the source channel has aliasoptindetourhost set). If the values of this attribute contain periods they will be compared against the list of potential detour hosts and the first host on the list that matches will be the chosen detour. If the value doesn't contain a period the first detour host will be used unconditionally.
ALIASDETOURHOST_NULL_OPTIN MTA option, which is similar to SPAMFILTERx_NULL_OPTIN (see Table 14–1. It specifies a special value which if used in the LDAP_DETOURHOST_OPTIN attribute is treated as the same as the attribute being omitted. The default value is "", which means that an empty attribute value is ignored.