blocked IP - can't email sbcglobal.net, att.net
Hello, we installed a new internet line at our company, unfortunately the public IP is being blocked by AT&T domains. We have already tried several times emailing firstname.lastname@example.org to unblock our IP, but got no reply. Our on-premise Exchange Server is secured, fully patched, and NOT sending any spam whatsoever. Reverse-DNS is also properly set up.
Who may I contact to get this resolved?