/etc/resolv.conf is fine - all DNS is working. I am puzzled where it gets 'yes.samantix.com' in the first place -- it is a non-existent server name in my domain, and the test email is being sent to a gmail.com address.
/var/log/zarafa/spooler.log, where the Connection Error is reported, is a Zarafa log -- maybe Zarafa is looking for yes.samantix.com as it's SMTP server/ postfix destination, but I don't know how or why.
/etc/zarafa/spooler.cfg includes the lines:
# Outgoing mailserver name or IP address
smtp_server = localhost