How to know from which email client the HTTP request was coming from? [duplicate]

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Email client detection

I have a newsletter which will have a link to my websites pages. Now i want to know which 开发者_如何学JAVAemail client (gmail, hotmail, outlook) the user opened the newsletter in and clicked the link to the website page.

The reason I want to know which email client, is because i want to customize the content in website pages based on the use of email client by users.

My Website pages will be coded in PHP

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Look at the User-Agent header ($_SERVER['HTTP_USER_AGENT']).

For users using webmails, the user-agent will be that of their browser; so you could look at the Referer header ($_SERVER['HTTP_REFERER']) too. (But notice that browsers don't send referer headers from https sites.)