My guess is that FreePBX distros will fight 'tooth and nails ’ your
iptables -A OUTPUT -d 37.49.230.74 -j DROP
/sbin/service iptables save
But I will guarantee the next vector will not be from 37.49.230.74
whois -h v4.whois.cymru.com ' -v -f 37.49.230.74'
gives the ASN of the ‘careless provider’. “ABC Consultancy”
If you go through your logs you will see these SQUITTER/ABC SQUATTERS have been probing FreePBX deployments for months, likely yours included (FYI, the real blackhats are not Dutch, nor Icelandic 
)