In my opinion the unique tag should be named after the service contract that is executed in it's behalf. In the case of forums it should be called "forums" and the additional information would contain items like "forum_id", "parent_id" (if in reply to something). Alternatively it would be "bounce" for the bounce management service contract. You should also keep in mind that you want to support multiple packages of one package type, so you need to pass on the package_id as well.
In addition to the default naming (e.g. forums, bounce, blogger), you should have a mechanism to define named special cases. E.g. you will map the "qanda" unique tag to the "forums" service contract with prefilled value for forum_id. For obvious reason, the user interface needs to be well thought through and we should *NOT* have to create the named special cases by going into the code.
Some more remarks based on previous challanges:
How do you make sure that all mails belonging to OpenACS are delivered to the mail-dir, but not the other mails, if you do not know which packages are installed? Wouldn't it make sense to have a prefix like "oacs" for each email address (incoming and outgoing) so that the MTA can differentiate between mailto:malte@sussdorff.de and mailto:oacs-malte@sussdorff.de, where the later goes to the "malte" package at the same domain ?
This is especially true if you want to allow easy postings to forums. The Email should be easy to remember (e.g. mailto:Forum-openacs_dev@openacs.org). Alternatively you can configure your MTA to try all other delivery methods first and only if all failed, store the Email in the maildir for OpenACS.
Furthermore, make sure you do not interfere between multiple installations of your mail-package on the same site. Therefore the system name (from your aolserver config) should make it into the mail scanning as well, to prevent server1 reading and storing mails destined for server2.
