any way to monitor sophos xgs mailspool length ?

Hello,

is there a way to monitor xgs mailspool externaly for using in checkmk or nagios or similar ?

i checked the web api, but there is nothing for displaying stats , seems to be only for setting things

https://docs.sophos.com/nsg/sophos-firewall/18.5/API/index.html

other way would be using snmp but also here is nothing to find 

https://docs.sophos.com/nsg/sophos-firewall/18.5/Help/en-us/webhelp/onlinehelp/AdministratorHelp/Administration/SNMP/index.html#mib-and-oids

connection to postgres db, but how ? 

so please give me some way to script something for this.