/log info "Loading MX ipv4 address list"
/ip firewall address-list remove [/ip firewall address-list find list=MX]
/ip firewall address-list
:do { add address=204.44.138.0/23 list=MX } on-error={}
:do { add address=208.78.16.0/22 list=MX } on-error={}