I informed them that the IP history has it blacklisted and their response:
"those are not reliable data sources"
I asked twice for the reliable source and they sent a link to www.senderbase.org/lookup/ (run by Cisco) which checks 4 blacklist databases in which indeed it is NOT listed.
Is it safe to ignore the blacklist reports in mxtoolbox.com and multirbl.valli.org? :)
By practice all my other IPs a clear in mxtoolbox.com, so just want to double check that this is safe to ignore.
Thanks