an alias and a primary email must always be unique

[tpokorra]

otherwise the login fails: alias xyz@myexample.org with account A and primary email xyz@myexample.org with account B: B cannot login

do debug this, see https://github.com/TBits/KolabScripts/wiki/Debugging-Authentication testsaslauthd -u ... -p ... and run with storeloginpwd enabled, see the storeloginpwd.file