Well... this is not as much about hiding your address as it is about making sure that you don't get spammed much later after registering for a site.

Still: I am not logging alias resolution. The SMTP-Server is not logging a thing. Insofar, if authorities would ask me to give them data, I plain couldn't if the alias has expired by then.

If the alias is still valid, then of course, I would have to comply, but see my first point.