What's new in 4.6:
*) only accept dotted decimal notation for IP addresses. Use of numbers
with leading zero, numbers larger than 255 and non-decimal numbers
is not accepted (but still can ommit third or second and third numbers,
if they are zero);
*) email - user must enable tls explicitly
*) remove limit on number of multicast enabled interfaces, maximum was 32;
*) dhcp server - show last-seen time for leases;
*) dhcp server - do not create busy lease if client declines all IP addresses;
*) fixed - when closing winbox terminal window with active serial-terminal
console command, serial port sometimes was left in acquired state;