Recently I had problems with my notes, which are synced via iTunes into my iPhone and Mail. I couldn’t make any new notes as well as no syncing too. What was wrong?

Recently I was doing a cleaning of my fonts folder and obviously deactivated one font to much. Reactivating the font MarkerFelt and everything was back to normal!

Alternative: Go to Mail Preferences and look for the tab Font & Color and chose a different font for your notes. (which is what I did, as I didn’t like the marker-font anyway.)