as a fix solution you can use google, as smtp relay for e.g. notifications. In this example I am working on a Fedora 27 Host.
Install needed packages
dnf -y install postfix mailx cyrus-sasl-plain
Restart and enable services
systemctl restart postfix && systemctl enable postfix
Adjust /etc/postfix/main.cf depends your needs (marked in red)
myhostname = zuerich.tuxclouds.org
relayhost = [smtp.gmail.com]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_tls_CAfile = /etc/ssl/certs/ca-bundle.crt
smtp_sasl_security_options = noanonymous
smtp_sasl_tls_security_options = noanonymous
Setup the secret
vim /etc/postfix/sasl_passwd
[smtp.gmail.com]:587 username:password
Issue the command postmap to read the new secret
postmap /etc/postfix/sasl_passwd
Set correct owner and permissons
chown root:postfix /etc/postfix/sasl_passwd
chmod 640 /etc/postfix/sasl_passwd
Reload the service
systemctl reload postfix
Verify the setup, by sending you a Test Notification Mail
echo "Test Mail" | mail -s "Test Notification Mail" [email protected]