I've been having this problem too. (Addresses without a "." in the name are rejected by the list as well.) Today I found that emails sent from the Mac OSX email client and Yahoo webmail (from subscribed addresses) were rejected by SmartList and forwarded to the maintainer. When I sent emails from the same addresses using the mail() function in a quick php script, the emails were accepted and distributed to the list. I have also experienced an email address/client suddenly stop working. My client had been using the lists created with SmartList for months (using MS Outlook, I believe) when his emails mysteriously stopped being accepted by the list and delivered to the maintainer only. I'd be happy to foward headers from accepted and rejected emails to anyone who might be able to help out. Thanks, Andy