The mail server could not deliver mail to david@xxx.com. The account or domain may not exist, they may be blacklisted, or missing the proper dns entries.

Solusi nya jika memang jika kirim dari domain lain / yahoo / gmail bisa kirim maka setting Exim nya sbb :

“WHM Home » Service Configuration » Exim Configuration Manager » Advanced Editor” lalu search ” Add Additional Configuration Setting “

dan tambahkan allow_mx_ip_ip = yes , lalu save ..