Can I have your IP address so that I can let you know where your IP has been blacklisted. The most important issue is that your emails start going into the spam. Checkout your IP on these websites as well: Abusix Mail Intelligence Blacklist, BARRACUDA, and ivmSIP. I personally faced this issue within my team. My websites got hacked by some Ru guys and they changed all the meta tags and even they run a email sending script, so we moved to another server and that IP was also get blacklisted instantly because of malwares. Our rankings get dropped and we are still recovering the same.