ok I'll reply to myself: it 'just works' !!
- installed smeserver-vacation with
yum --enablerepo=smecontribs install smeserver-vacation
- went to the control panel
- found panel "user vacations"
- edited message for maillog user.
Attention, it says in the text above the message to put a white line between headers and message text. if you don't, all text goes into the subject..
- enabled the vacation message with "yes" under the message:
IT JUST WORKS!!
I must say, this is the time I love SME most. Thank you a lot, devs! Thank you, thank you all.
ciao, Michel