Increased proxy timeout to prevent proxy timeout like issue #1473 - Can't add e-mail account in e-mail channel configuration.

contrib/nginx/zammad_ssl.conf

@@ -134,7 +134,7 @@ server {
         proxy_set_header CLIENT_IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         proxy_set_header X-Forwarded-Proto $scheme;
-        proxy_read_timeout 180;
+        proxy_read_timeout 300;
         proxy_pass http://zammad;
 
         gzip on;