You have to check your MX records,MX must point to mailcow server ,also check reverse proxy settings

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    posixaz

    I have only one public IP. The mailcow server uses the same public IP of server1. Also namecheap does not allow IP, only domain e.g. mail.,ydomain.com

    ,also check reverse proxy settings

    the reverse proxy works, I can access mailcow interface from external networks. The problem is only when recieving emails from external networks.

        posixaz

        This is what my reverse proxy in server1 one looks like looks like:
        `

        server {

   server_name mail.mydomain.com;

   listen 25;
   listen 465;
   listen 587;
   listen 143;
   listen 993;
   listen 110;
   listen 995;
   listen 4190;

    proxy_set_header   X-Real-IP $remote_addr;
    proxy_set_header   X-Scheme $scheme;
    proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header   X-Forwarded-Proto $scheme;
    proxy_set_header   X-Forwarded-Port $server_port;
    proxy_set_header   Host $http_host;

   location / {
     proxy_pass http://local_ip_mailcow_server/;
   }

listen [::]:443 ssl; # managed by Certbot
listen 443 ssl; # managed by Certbot
ssl_certificate ...letsencrypt/live/...
ssl_certificate_key ...letsencrypt/live/...
include ...letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam ...letsencrypt/ssl-dhparams.pem; # managed by Certbot
 }
 server {
     if ($host = mail.mydomain.com) {
       return 301 https://$host$request_uri;
   } # managed by Certbot
   listen 80;
   listen [::]:80;
   server_name mail.mydomain.com;
   return 404; # managed by Certbot
  }

        `

            idhamari you can try telnet from outside to your 25 port to prove is your postfix-mailcow 25 port accessible from outside

              I got this using: telnet public-ip

              telnet: Unable to connect to remote host: No route to host

              and I got this using nmap -sS public-ip

              PORT STATE SERVICE
              25/tcp open smtp
              80/tcp open http
              110/tcp open pop3
              143/tcp open imap
              443/tcp open https
              465/tcp open smtps
              587/tcp open submission
              993/tcp open imaps
              995/tcp open pop3s

              telnet public-ip 25

              I got Connected to public-ip
              Escape character is ‘^]’.

              you have to see your smtp greeting banner like

              220 your server ESMTP Postcow

              16 days later

              I fixed the nginx but I still have the same behavior.

              I can send/receive to/from mailcow to mailcow
              I can send to google but not recieve with this error:

              The response from the remote server was:
530 5.7.1 Authentication required

              I can not send/recieve from yahoo

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