From some addresses it's impossible to post into a smartlist

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