I'm using EFA as a smarthost for Exchange. I found this Message at the efa admin site: (host relay.rzone.de[81.169.145.96] said: 450 4.1.0 Don't use the Backup MX 'relay.rzone.de' while the Primary MX is available - please send your mail to xx.xxxxxx.xx [xxx.xxx.xxx.xxx] (in reply to RCPT TO command...