And yet 2 million people use Yahoo groups.
I just think it is ridiculous how for 10 years, people have tried to minimize, marginalize, and ignore a customer base that is holding steady at those numbers. When you are running a business, do you pick and choose which customers you want to serve based on whether they are tall, fat, cute, ugly, male, female, etc.?
The hardest part of Post by Email would be writing/licensing/adapting mail server software to *receive* and parse e-mail. But this would pay dividends in being able to support e-mail bounce management out-of-the-box, which in turn would make XenForo less likely to get blacklisted by mail servers.