Archie, on further investigation it appears that QBO have had this blacklist issue with their IP address in the past - see thread 

Intuit IPs found in Spamcop blocking list preventing vendors from sending invoices

What is worrying is that it takes your IT dept months (one person said over 6 months) to get this rectified. I hope that information is not correct and your IT dept can simply follow the steps that my host provider has given and solve this issue.