if FEATURE('authinfo') is used, then the hostname in the map entry must match exactly the hostname of the ISP mailserver
Veja no seu SMART_HOST + informações para o cliente
What is "U:", really?
Bem, Autenticação SMTP está em inglês puro
U user (authorization) id
I authentication id
...
User or authentication id must exist as well as the password. All other entries have default values. If one of user or authentication id is missing, the existing value is used for the missing item.