Hello, we have posted a design for multi-domain list manager: here
Understanding the possible limitation of not having access to master.cf as well as the necessity that all incoming mail be routed through mail-in.pl, it seems logical to do the routing in mail-in.pl.
What I conceive is to have a configuration option in mail-in.pl which directs it to consider multiple domains.
The values of the configuration option (ie: routing_type) will be directives indicating behavior (ie: NONE, LOCAL, DATABASE).
NONE will be the default and will provide the present behavior of honoring the mail.conf to do the appropriate database inserts for the incoming mail.
LOCAL indicates that the localhost has multiple drupal instances on unique domains. The LOCAL directive will use the domainname of the incoming message to determine which version of mail.conf to employ for performing the necessary inserts (ie: example.com:mail.conf).
DATABASE indicates that the domains are not co-located and the message must be forwarded 'off host'. DATABASE will instruct mail-in.pl to query to discover the appropriate receiving host details. (Table definition to be determined)
Too, there is the complexity of validating user's by consulting the og2list_groups table for each of the configured domains. Presently, this is a function of the condition = tag in the .cf file. To achieve this, the validate-recipient.pl script could be required for multi-domain configurations wherein the script is modified to support the LOCAL and NONE routing_type directives.
We are looking for reviews and support to get this built.
Kieran