Postal isn't send to relay smtp i set.

[Gangmi]

Hello, I tried to using Postal with API call.
I just want postal sending email only.

First, What i want Configuration diagram is

====closed network==== | === public network ====
(DNS Look up unavailable) | (DNS Look up available)
SMTP Client -----> Postal -----> relay(Postfix) --------> receiver
(API)

When i call API, The error is No SMTP servers were available for gmail.com No hosts to try.
I think Postal isn't send to relay smtp i set.
The reason why I think so is because Postfix test was normal(I sent smtp request in closed network SMTP clinet to Postfix )
And there is no received logs in Postfix..

In this situation, what can i do?
And i just set configuration

An array of SMTP relays in the format of smtp://host:port
smtp_relays: []

Is there anything i set?

[willpower232]

No SMTP servers were available for

This means that Postal was unable to connect so either your Postal server couldn't look up the DNS records or there was some kind of firewall blocking the access which could also include your server provider blocking email.

If you're trying to relay all email via your postfix, have you set that up in the config file?

[Gangmi]

Hello, willpower
As i said question, I just set the configfile's - smtp_relays: [smtp://myhost:25]
I want all email via my postfix. Is there any config for your answer? => "If you're trying to relay all email via your postfix, have you set that up in the config file?"

[willpower232]

are you still having problems with that? did you just need to restart after changing the config file? sounds like you have everything so if you're still having problems then there must be a firewall or network issue

[Gangmi]

Unfortunately, it doesn't work...
What I want to know is if there are any other settings that send all smtp requests to the relay server other than what I did (smtp://host:port).
It is confirmed that the firewall from the closed network to the public network is already open (the Telnet is also connected and requests are sent from the closed network to the postfix on the public)
However, the problem is that it can't even reach the postfix only when I request an API to send an e-mail to the postal