do they keep track after every ip adress of all users at all times
Certainly in the UK, every email has to be stored by the ISP for a certain length of time, by law. So all the header information is accessible. The ISPs also have to archive their log files for a similar period, so anything / anyone can be traced.
Can't speak for the rest of the world though - I'm sure there are still some shady nooks and crannies available for ne'er-do-wells to hang out.
SD