How to just receive emails through action mailbox?

Hi, I am currently testing and setting up an email service system.

I just need to be able to receive emails ， but no need to send email.

1. my dns mail.xxx.com is ping successful, it can get bytes from IP address.

2. My online-server had open port： 443，22， 109，110， 993，995

3. I used docker to deploy my rails server.

Dockers proxy ports is: 443, 109,110,993,995 and rails server port is 3005

1. My ApplicationMailbox and comments_mailbox like this:

class ApplicationMailbox < ActionMailbox::Base

  routing /@xxx.com/i => :comments
  routing :all => :comments
end

class CommentsMailbox < ApplicationMailbox
  def process
    p mail.decoded
  rescue => e 
    p e
  end
end

1. My nginx configuration is like this:

user xxx;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;
events {
  worker_connections 1024;
}
mail {
  server_name mail.xxx.com;
  ssl on;
  ssl_certificate xxx.pem;
  ssl_certificate_key xxx.key;
  ssl_session_timeout 5m;
  ssl_protocols ...;
  ssl_ciphers ....;
  ssl_prefer_server_ciphers on;
}
http {
  ...
}

When I send email from gmail account to ydddd@xxx.com (my custom emails), I can't receive email in production.

I had see this video : https://gorails.com/episodes/action-mailbox-rails-6, but it seems can not help me.

If I just want to receive emails in rails, What should I to do ? Was I need to use third party api such as sendgrid or Mailgun
?

Thanks so much~~