At Clouding, we receive SPAM reports about some of our IPs used by our customers. This is because a large amount of SPAM has been detected coming from a specific IP.
There are SPAM lists called RBLs, which are SPAM blacklists. If you want to know whether a server's IP is on a SPAM list or blacklist, there are many websites you can check. We usually recommend two specific websites that show very clearly whether an IP is listed or not:
One of them is Vali.org where a listing is displayed in which the SPAM list your IP has been added to will appear in black. Generally, there is a link where, after resolving the SPAM problem, you can submit another notification to have yourself removed from that listing. If you have resolved the problem correctly, you will be removed from that list after some time.