I work on a saas application and we use sparkpost to communicate with clients from our product however some of our platform emails are not reaching our users, particularly those using outlook or hotmail. In Sparkpost the bounce report shows the following information: 550-"JunkMail rejected - mta# [a.b.c.d]:55522 is in \n550 an RBL, see Blocked - see http://www.spamcop.net/bl.shtml?a.b.c.d"
I have tried to understand what the issue is but am not very experienced in this domain. Can someone please help or make a recommendation of where I might be able to find help?
Thanks in advance for your time.