For evaluation i tried to use masquerading in the sendmail.cf.
But it seems that the scalix does not use this setting, instead it is using
"the first" entry in the users internet-adress list.
I tried this to have a new mailbox user@scalixtest.mydomain.com on the testmachine
to receive mails, but send mails as user@mydomain.com
Is ther an other solution ?