#smtp.isp.com username:password
smt`p.mydomain.com send-user@mydomain.com:mySecretePassword
chown root:root /etc/postfix/password
chmod 0600 /etc/postfix/password
postmap hash:/etc/postfix/password
relayhost = smtp.mydomain.com:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/password
smtp_sasl_security_options =
systemctl restart postfix
dnf install cyrus-sasl cyrus-sasl-lib cyrus-sasl-plain
smtp_enforce_tls = yes
smtp_tls_security_level = encrypt
systemctl restart postfix
sender_canonical_maps = regexp:/etc/postfix/canonical
vi /etc/postfix/canonical
/^.*localhost.*/ send@mydomain.com
/^.*localdomain.*/ send@mydomain.com