Mail Rejected

the smtp server have ptr/a records setup, smtp auth enabled, isn't on any blacklist and never was. when sending mails to certain recipients mail returns with 554 error stating the ip is blacklisted. the referencing ip is dynamic ip used by sender, not the server itself. i inspected the headers and server ip is listed in one of the from fields, the client ip is listed under another from fields.

how do i prevent this error from happening? i don't want to relay my smtp server which is perfectly fine to isp smtp server. why isn't the receiving smtp checking the last from field which is server's ip but instead bounce the message because the client is on dynamic ip?

if you have any solution, please share, regardless of the mta you're using. i'll make the appropriate changes in my configuration. i'm thinking it's not my fault but receiving smtp fault because i can send using the same configuration to some other recipients who have spamhaus checking enabled and everything works fine because the server checks on the my server ip and not on the client's ip.