什么是“用户代理”？在 codeigniter 电子邮件库的配置中？
我可以看到 codeigniter 的电子邮件库的 useragent 正如文档所述是可以更改的。
但useragent到底是什么？它对我们有什么作用？
I can see that the codeigniter's email library's useragent is changeable as the document says.
But what is really the useragent and what does it do for us?
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我不确定电子邮件库的情况，但在大多数情况下，用户代理是用户“使用”以浏览器类型/版本、操作系统类型/版本等方式发出请求的标识符。
此信息是常用或包含的cookie。
以下是用户代理的示例：
Mozilla/5.0（iPad；U；CPU OS 3_2，如 Mac OS X；en-us）AppleWebKit/531.21.10（KHTML，如 Gecko）Version/4.0.4 Mobile/7B334b Safari/531.21.102011 -10-16 20:23:50
Mozilla/5.0（iPad；U；CPU 操作系统3_2，如 Mac OS X；en-us) AppleWebKit/531.21.10（KHTML，如 Gecko）版本/4.0.4 Mobile/7B334b Safari/531.21.102011-10-16 20:23:10
Mozilla/5.0（Windows NT 6.1）魔兽世界64； Gecko/20100101 Firefox/7.0.12011-10-16 20:23:00
Mozilla/5.0（Linux；U；Android 2.3.3；en-au；GT-I9100 Build/GINGERBREAD）AppleWebKit/533.1（KHTML，如 Gecko）版本/4.0 手机版Safari/533.12011-10-16 20:22:55
Mozilla/4.0（兼容；MSIE 7.0；Windows NT 5.1；InfoPath.2；.NET CLR 2.0.50727；.NET CLR 3.0.04506.648；.NET CLR 3.5.21022； .NET CLR 1.1.4322)2011-10-16 20:22:33
Mozilla/5.0 (Windows NT 6.1; rv:5.0) Gecko/20100101 Firefox/5.02011-10-16 20:21:42
Mozilla/5.0 (Macintosh; Intel Mac OS) X 10_7_2) AppleWebKit/535.1（KHTML，如 Gecko）
Chrome/14.0.835.202 Safari/535.12011-10-16 20:21:13
Mozilla/5.0（黑莓；你；黑莓9800； en) AppleWebKit/534.1+（KHTML，如 Gecko）版本/6.0.0.337 Mobile Safari/534.1+2011-10-16 20:21:10
Mozilla/5.0（兼容；MSIE 9.0；Windows NT 6.1；WOW64；Trident/5.0 )2011-10-16 20:21:07
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:7.0.1) Gecko/20100101 Firefox/7.0.12011-10-16 20:21:05
Mozilla/5.0 (X11; Linux i686) AppleWebKit/534.34 (KHTML，如 Gecko ) 雷孔克Safari/534.342011-10-16 20:21:01
Mozilla/4.0（兼容；MSIE 8.0；Windows NT 6.1；Trident/4.0；GTB6；SLCC2；.NET CLR 2.0.50727；.NET CLR 3.5.30729；.NET CLR 3.0.30729； PC 6.0；OfficeLiveConnector.1.3)2011-10-16 20:20:48
BlackBerry8300/4.2.2 配置文件/CLDC-1.1 VendorID/107 UP.Link/6.2.3.15.02011-10 -16 20:20:17
IE 7？ Mozilla/4.0（兼容；MSIE 7.0；Windows NT 5.1；.NET CLR 1.1.4322；.NET CLR 2.0.50727；.NET CLR 3.0.04506.30）2011-10-16 20:20:09
Mozilla/5.0（Windows； U；Windows NT 6.1； rv:1.9.2.23) Gecko/20110920 Firefox/3.6.23 SearchToolbar/1.22011-10-16 20:20:07
I'm not sure about the email library's case, but in most cases the useragent is the identifier of what the user "used" to make a request in the way of the browser type/version, OS type/version, etc.
This information is commonly used or contained cookies.
Here are examples of useragents:
Mozilla/5.0 (iPad; U; CPU OS 3_2 like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Version/4.0.4 Mobile/7B334b Safari/531.21.102011-10-16 20:23:50
Mozilla/5.0 (iPad; U; CPU OS 3_2 like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Version/4.0.4 Mobile/7B334b Safari/531.21.102011-10-16 20:23:10
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:7.0.1) Gecko/20100101 Firefox/7.0.12011-10-16 20:23:00
Mozilla/5.0 (Linux; U; Android 2.3.3; en-au; GT-I9100 Build/GINGERBREAD) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.12011-10-16 20:22:55
Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; InfoPath.2; .NET CLR 2.0.50727; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; .NET CLR 1.1.4322)2011-10-16 20:22:33
Mozilla/5.0 (Windows NT 6.1; rv:5.0) Gecko/20100101 Firefox/5.02011-10-16 20:21:42
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_2) AppleWebKit/535.1 (KHTML, like Gecko)
Chrome/14.0.835.202 Safari/535.12011-10-16 20:21:13
Mozilla/5.0 (BlackBerry; U; BlackBerry 9800; en) AppleWebKit/534.1+ (KHTML, like Gecko) Version/6.0.0.337 Mobile Safari/534.1+2011-10-16 20:21:10
Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)2011-10-16 20:21:07
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:7.0.1) Gecko/20100101 Firefox/7.0.12011-10-16 20:21:05
Mozilla/5.0 (X11; Linux i686) AppleWebKit/534.34 (KHTML, like Gecko) rekonq Safari/534.342011-10-16 20:21:01
Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; GTB6; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; OfficeLiveConnector.1.4; OfficeLivePatch.1.3)2011-10-16 20:20:48
BlackBerry8300/4.2.2 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/107 UP.Link/6.2.3.15.02011-10-16 20:20:17
IE 7 ? Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30)2011-10-16 20:20:09
Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.23) Gecko/20110920 Firefox/3.6.23 SearchToolbar/1.22011-10-16 20:20:07