First time setting up a mail server, first time major issue:
Testing the SMTP or IMAP results in a 504 status code after some time
I've followed this guide for roundcube: https://www.linuxbabe.com/ubuntu/install-roundcube-webmail-ubuntu-20-04-apache-nginx (https://www.linuxbabe.com/ubuntu/install-roundcube-webmail-ubuntu-20-04-apache-nginx)
furthermore use:
   - debian 10 (Buster)
 - nginx 1.14.2
 - postfix 3.4.14
 - dovecot 2.3.4.1
 - roundcube 1.4.8
 
sudo nano /etc/nginx/sites-enabled/webmail.exampledomain.com
server {
        if ($host = webmail.exampledomain.com) {
                return 301 https://$host$request_uri;
        }
        listen 80;
        listen [::]:80;
        error_log /var/www/webmail.exampledomain.com/logs/error.log error;
        access_log /var/www/webmail.exampledomain.com/logs/access.log;
        server_name webmail.exampledomain.com www.webmail.exampledomain.com;
        return 404;
}
server {
        listen 443 ssl;
        listen [::]:443 ssl;
        ssl_certificate /etc/letsencrypt/live/webmail.exampledomain.com/fullchain.pem; # managed by Certbot
        ssl_certificate_key /etc/letsencrypt/live/webmail.exampledomain.com/privkey.pem; # managed by Certbot
        include /etc/letsencrypt/options-ssl-nginx.conf;
        ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem;
        server_name webmail.exampledomain.com www.webmail.exampledomain.com;
        index index.php index.html index.htm;
        root /var/www/webmail.exampledomain.com/html;
        error_log /var/www/webmail.exampledomain.com/logs/error.log error;
        access_log /var/www/webmail.exampledomain.com/logs/access.log;
        client_max_body_size 10m;
        location ~ \.php$ {
                include snippets/fastcgi-php.conf;
                fastcgi_pass unix:/run/php/php7.4-fpm.sock;
                fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
                include fastcgi_params;
        }
        location ~ /\.ht {
                deny all;
        }                                                                                                                                                                                                          
        location ~ /.well-known/acme-challenge {
                allow all;
        }
        location ~ ^/(README|INSTALL|LICENSE|CHANGELOG|UPGRADING)$ {
                deny all;
        }
        location ~ ^/(bin|SQL)/ {
                deny all;
        }
    add_header Strict-Transport-Security "max-age=31536000" always; # managed by Certbot
    ssl_trusted_certificate /etc/letsencrypt/live/webmail.exampledomain.com/chain.pem; # managed by Certbot
    ssl_stapling on; # managed by Certbot
    ssl_stapling_verify on; # managed by Certbot
}
*Testing IMAP login*
(https://i.imgur.com/OosMsDt.png)
then:
sudo tail /var/www/webmail.exampledomain.com/logs/error.log
2020/08/27 16:43:31 [error] 2236#2236: *73 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 162.158.159.14, server: webmail.groote.xyz, request: "POST /installer/index.php?_step=3 HTTP/1.1", upstream: "fastcgi://unix:/run/php/php7.4-fpm.sock", host: "webmail.groote.xyz", referrer: "https://webmail.groote.xyz/installer/index.php?_step=3"
Does anyone know why I am receiving a 504 status code?
I will happily provide more config files 
			
 
			
			
				Error message was pretty straight forward. The file "fastcgi://unix:/run/php/php7.4-fpm.sock" could not be accessed because file "/run/php/php7.4-fmp.sock" did not exist. 
creating the file with:
sudo nano /run/php/php7.4-fmp.sock 
ctrl + o -> enter -> ctrl + x
restart the php7.4-fmp service:
sudo systemctl start php7.4-fpm.service
Check if everything works with:
sudo systemctl status php7.4-fpm.service
also these files have been created by the service:
/run/php/php7.4-fpm.pid
/run/php/php7.4-fpm.sock
/run/php/php-fpm.sock