I am moving some of the "settled" discussion here, I hope that is appropriate. --DavidBremner

I wonder if it would be more or less natural to put an encoded form of the page name in the email address? I'm thinking about something like wikiname+index@host or wikiname+todo+comment_by_mail@host. The basic transformation would be to call titlepage($page) (in the C locale), followed by replacing "/" with "+" (since "/" is not valid in mails). --Joey

I guess you are right, there is no point being more obscure than necessary. I am leaning towards something not
calling titlepage but in the same spirit. --DavidBremner

In response to the suggestion by Joey to process mailboxes into blogs

One thing it made me think about is how to encode reference (threading) information. One can of course encode this into local-part, but I wonder if it would be better to use header features of mailto (this could also be an alternative to tagged mail addresses for page references).
Various client handling of mailto always seemed a bit fragile to me but maybe I am just behind the times. Most headers are ignored, but pseudo-headers in the body might work. For example: test. I hesitate to use the subject because every mail admin in the world seems to want to add things to the front of it. -- DavidBremner