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Continue to ChatQuery : Support of If-Modified-Since HTTP header I'm not sure if this is better in this forum or in the Server Fault forum... On Google Webmaster Guidelines I see this: "Make sure your web server supports https://vmapp.org/query/83024/Support-Of-If-Modified-Since-HTTP-Header-I-M-Not-Sure-If-This-Is-Better-In-This-Forum-Or-In-The-Server-Fault-Forum-On-Google-Webmaster-Guidelines-I-See-This-Make-Sure-Your-Web-Server-Supports/