Postfix - relay trough other smtp server with email authorization

To relay our mail from a home/office server trough real mail server, that has all needed stuff like PTR, SPF, DKIM etc. stuff setup, the easies way is to 'login' to a free, open service like gmail, yahoo etc. server and send from our account there.
So, let's do this with postfix.
The EASY way to do is, if the provider supports submission protocol (port 587).
Then in we set a relayhost

relayhost = []:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_CAfile = /etc/postfix/cacert.pem
smtp_use_tls = yes

then we create /etc/postfix/sasl_passwd:


we create hash file:
#> postmap /etc/postfix/sasl_passwd

then we make:
#> chmod 400 /etc/postfix/sasl_passwd*
and then
#> /etc/init.d/postfix restart
#> systemctl restart postfix (8 and above)

The HARD way is to do it with stunnel program.
We should do this ONLY if provider supports only ssl smtp connection.

Make sure stunnel is installed:
#> apt-get install stunnel4

First, make same steps as above BUT relayhost is with other valie:
then in /etc/postfix/ check

relayhost =

After setting relay to localhost at random port, we setup stunnel.
We create /etc/stunnel/
It holds this:

client = yes
chroot = /var/lib/stunnel4/
setuid = stunnel4
setgid = stunnel4
pid = /
socket = l:TCP_NODELAY=1
socket = r:TCP_NODELAY=1

accept =
connect =

Then, we restart stunnel and postfix and we are ready.