Es un conflicto de versión de Windows.
Exim Configuration Manager
Security
SSL/TLS Cipher Suite List
Require clients to connect with SSL or issue the STARTTLS command before they are allowed to authenticate with the server................ NO
OFF - Introduce a delay into the SMTP transaction for unknown
whm hostname host.domain ip.... cloudflare + cp.enteministry
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problema: 503 Valid RCPT Command mus
solución a: activar authentificaciónsolución b: swich cpanel, mail routing, local