Email goes to spam even with valid SPF, DKIM and DMARC records, dynamic rDNS on AWS instance

I have an instance on AWS and fighting with sending emails through cPanel. All records are OK (checked on MX toolbox): SPF, DKIM, DMARC at the cPanel level and the WHM level (hostname). Even rDNS is OK. Server IP is not flagged or blacklisted (checked on MX toolbox). Email deliverability is OK both on WHM and cPanel. The header that I received actually says some interesting things. But how to resolve this rDNS problem? It looks to me that this is the default AWS setup for an instance. See in 2.6 RDNS_DYNAMIC and HELO_DYNAMIC_IPADDR below: Content analysis details: (6.8 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 SPF_PASS SPF: sender matches SPF record 0.7 HTML_IMAGE_ONLY_20 BODY: HTML: images with 1600-2000 bytes of words 0.0 HTML_MESSAGE BODY: HTML included in message -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain 0.5 KAM_NUMSUBJECT Subject ends in numbers excluding current years 2.6 RDNS_DYNAMIC Delivered to internal network by host with dynamic-looking rDNS -0.0 T_SCC_BODY_TEXT_LINE No description available. 3.2 HELO_DYNAMIC_IPADDR Relay HELO'd using suspicious hostname (IP addr 1) 0.0 T_REMOTE_IMAGE Message contains an external image X-Spam-Flag: YES