Hi Falko, thanks for your reply,
Let me go on the learning...
Sorry, it may sound silly questions but as I have been learning by myself it is very challenging :-)
My local internet provider is www.tpa.com.br
( brasilian )
What is the file's name to type in below lines, please?
postconf -e 'relayhost = smtp.tpa.com.br'
postconf -e 'smtp_sasl_auth_enable = yes'
postconf -e 'smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd'
postconf -e 'smtp_sasl_security_options ='
#--- below - my internet provider + user at this proivder + pass = correct ?
echo "smtp.tpa.com.br ewb1:1234567" > /etc/postfix/sasl_passwd
chown root:root /etc/postfix/sasl_passwd
chmod 600 /etc/postfix/sasl_passwd