Fix bug when sending notification emails. Currently emails are send from user 'nut' which can't be resolved by postfix.

git-svn-id: http://svn.code.sf.net/p/openmediavault/code/trunk@1510 3c3d7b80-5828-415e-9f61-280b98178fff
Improve code.

git-svn-id: http://svn.code.sf.net/p/openmediavault/code/trunk@1511 3c3d7b80-5828-415e-9f61-280b98178fff