@Patrick, HSTS is enabled/disabled on a per-domain basis, you can find that in Options for the domain.
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The built in webserver does by default sets some important settings that are needed for some protocols to function correctly, you don't need to ANY configuration if you use the built in server.
For NGINX these options are
# Buffer settings
proxy_buffer_size 4096k;
proxy_buffers 8 4096k;
proxy_busy_buffers_size 4096k;
# Timeouts
proxy_connect_timeout 1200s;
proxy_send_timeout 1200s;
proxy_read_timeout 1200s;
These timeouts are important because protocols like MAPI and EWS use long-standing web requests to detect changes. These values might be excessive as well, not a ton of testing was done yet on NGINX or Caddy besides getting it working.
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If you have no strong reason to be using Apache, Nginx, etc, you'll have a much easier time just using the built in webserver. It's Kestrel, Microsoft has been working hard on it, it performs REALLY well, and we have direct control over it. We're using it in our production.
Matt Petty
Senior Software Developer
SmarterTools Inc.