As of now the code does not check this. But it is a more or less quick hack for the proof of concept. What you do want to do is get the code out from there and write a callback for incoming_email. Just make sure that the email given for a group does not start with a prefix used by any other installed package.
Or maybe I should just write an additional callback for the incoming email like "incoming_email_matched_party" which could then be used for this.
It would allow each of the package do do what it likes. E.g. dotlrn could define that only administrators can write to the .LRN group while acs_subsite checks if the user is a member of the group (and it is not a .LRN group). And my custom application would deal with it differently.
Which brings me to the question: Can an implementation of a callback stop the further execution of other implementations? E.g. if my callback implementation "aa_malte" has successfully dealt with the e-mail I do not want any other callback implementations to be executed.
