IP address authorization issues often stem from a combination of factors related to your ISP's policies, your IP's reputation, and proper technical configuration. A key reason is being listed on the PBL (Policy Block List), indicating your ISP prohibits direct sending from that IP range, requiring you to engage with them directly. A poor IP reputation, frequently caused by spam-like activity, is another significant contributor; resolving this involves cleaning up sending practices, implementing email authentication (SPF, DKIM, DMARC), and requesting delisting from blacklists. Further, PTR records play a crucial role by associating your IP with a hostname, which is essential for deliverability. Maintaining good sending practices is essential to prevent your IP from being flagged, which may involve implementing practices.