# WarnAt needs to be at what percentage you want to be warned you are running out of IP addresses.
:local WarnAt 10
#Name of DHCP Pool you want to monitor
:local DHCPPoolName dhcp_pool1
#Your Email to notify you when running out of available ip's
:local Email my@email.com
#Your mail server ip address
:local EmailServer 0.0.0.0

#Declare Variable
:local Total

:foreach i in=[/ip pool get $DHCPPoolName ranges] do={
#Get the DHCP pool range and put into a string.
:local range [:tostr $i]
#Get the Start address of the range
:local Start [:pick $range 0 [:find $range "-"]]
#Get the End address of the range
:local Stop [:pick $range ([:find $range "-"] + 1) 31]
#Calculate how many IP's are in the Pool by subtracting the end address and the start address and add one.
:local ip ($Stop - $Start +1 )
#Save the size of the pool to Total
:set Total ($ip + $Total)
}

#Get the name of the Server that is using the Pool
:local Server [/ip dhcp-server get [/ip dhcp-server find address-pool="$DHCPPoolName"] name]
#Get the number of IP address's used in the pool
:local Used [/ip dhcp-server lease print count-only where server=[/ip dhcp-server get [/ip dhcp-server find address-pool=$DHCPPoolName] name]]
#Subtract used from total to get available
:local Available ($Total - $Used)
#Calculate percentage IP's available
:local Perc (($Available * 100) / $Total)
#Setup e-mail
:local Subject ([/system identity get name] . " DHCP pool is at $Perc")
:local Body ("Out of $Total addresses you have $Available available")

#Send out Email when available ip's percentage is below or equal to warnat
:if ($Perc <= $WarnAt) do={
  /tool e-mail send to=$Email subject=$Subject body=$Body server=$EmailServer
}
:log info $Body