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Em Configurações SMTP > > Nome de anfitrião. Altere a configuração do nome do host para ser o rDNS do endereço IP público.
It does not matter what host name you enter, as long as it resolves to the IP address where hMailServer is running. You may have 15 different host names which resolves to the IP address hMailServer is running on. If this is the case, you can enter any of these 15 different host names in the Host name field.