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Mark -- I'm thinking that we need some way to distinguish between the system-generated notification and a message with the #file or #wiki added by a subscriber.
In the former case, I might want to mute it, or set it to No Email, or set the Topic Duration to one hour or some such, so it doesn't reside forever in the message archive. In the latter case I would want it to go through to the subscribers immediately and remain forever in the archive.
Currently, the only way available to manage this is to put the hashtag on moderation, which not only increases moderator workload (re: Patti's problem with wiki updates) but also delays the posting of desirable messages.
If we're going to use system hashtags for this, we're going to need some way to keep subscribers from using them (and optimally, keep them off the "top hashtags" list). Since bouncing incoming emails that might by chance contain a reserved hashtag seems rather harsh, I suggest they simply be stripped.