[RoundCube Users] Sending mail fails

Hi there,

Recently installed a new copy of roundcube on a new server. I currently have a working install on another machine, which works like a charm. (using it right now actually) Now when I try to send mail on the new server, I get a "Sending Failed" message. This new server runs postfix/courier-imap, and is perfectly able to send mail via telnet. The error I get in my syslog when trying to send via is this:

Feb 1 02:51:09 navi postfix/sendmail[11922]: fatal: usage: sendmail [options]

I've tried sending mail via the new box with multiple imap clients, both webbased and desktop based, and all of them work flawlessly. Any suggestions?

Server is running: Debian Stable / Postfix / Courier-imap

Thanks in advance,

Michiel Oosterling