Mailhog not working with nginx proxy_pass

Websocket configuration added to nginx.conf fixed issue.

See:

- https://www.nginx.com/blog/websocket-nginx/
- mailhog/MailHog#117

Also fixed ENV variable for MailHog. Should be HOSTNAME. More-less just
cosmetic change - used for EHLO/HELO & mail header. Default value is
mailhog.example.

remp/remp#149

Docker/nginx/nginx.conf

@@ -122,6 +122,12 @@ server {
     }
 }
 
+# Required by websocket configuration (see mailhog server configuration)
+map $http_upgrade $connection_upgrade {
+    default upgrade;
+    '' close;
+}
+
 upstream mailhog.remp.press {
         server mailhog:8025;
 }
@@ -131,5 +137,13 @@ server {
 
     location / {
         proxy_pass http://mailhog.remp.press;
+
+        # Websocket configuration
+        # See:
+        #  - https://www.nginx.com/blog/websocket-nginx/
+        #  - https://github.com/mailhog/MailHog/issues/117
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection $connection_upgrade;
     }
 }

docker-compose.yml

@@ -36,7 +36,7 @@ services:
   mailhog:
     image: "mailhog/mailhog:v1.0.0"
     environment:
-      MH_domainname: "mailhog.remp.press"
+      MH_HOSTNAME: "mailhog.remp.press"
 
   adminer:
     build: "./Docker/php"