Very strange problem...When using RC mail to send to exchange server the messages are getting a really high spam score and being deleted I think it has something to do with the information in the message header. I don't know, weird. I adjusted the config file to put a little more information into the header when i looked at the message propertys it was saying friom 9878779789@localhost as the message ID i think maybe that was throwing it off.
If so, it has been improved in 0.4.1. Changeset 3923 ? Roundcube Webmail (http://trac.roundcube.net/changeset/3923)
Sweet....Thx