网站应用中向客户发送邮件是常见的一个功能。SMTP协议貌似简单,而且资料繁多,但要彻底搞清楚客户端服务器之间的身份和关系处理,也不是件容易的事。
本文简明扼要对smtp交换过程中身份和条件进行说明,使初次接触smtp开发的能有个清晰的处理思路。错误之处请多指正。
先说说smtp的基本原理, 邮件客户端(outlook)和发送方smtp服务器之间, 发送方smtp服务器和接受方smtp服务器之间,走的都是smtp协议.
先说说我们最常见的情况:用outlook发邮件,从 admin@scutephp.com 发往 to@scutephp.com。 outlook里写好邮件后发送,会连接到帐号里登记的smtp服务器25端口,开始smtp会话:
mail from:
admin@scutephp.com服务器发现邮件的mail from 是本域的(linuxidc.com),这种情况下smtp服务器一般需要验证用户身份,验证通过提交邮件,邮件进入服务器的发送队列。 服务器投递邮件的进程或线程,扫描发送队列,取出邮件后分析要往哪发。 服务器发现邮件是发往 linuxidc.net,不是本域,先通过dns服务器查询 to@scutephp域的mx记录,假设为 smtp.scutephp.com,邮件投递进程连接 smtp.scutephp.com 的25端口,开始smtp会话
mail from:
scutephp.com服务器判断邮件是来自别的域,发往本域,所以不需要验证用户。不过有可能的情况是scutephp.com服务器先检查一下发信服务器的ip地址,和mail from 里的域名对应的mx记录是否匹配,不匹配的拒收。如果没有符合什么拒收条件,那么scutephp.com手下这封信,放入rose的邮件夹,rose可以通过pop3收取邮件。
如果 scutephp.com发送邮件失败的话,邮件进入发送失败队列,可能直接扔掉,或者再试着重发n次,如果都不成功,会通知发件人或别的什么,这要看服务器的处理。
现在再说说php发邮件,首先要搞清楚,要用什么身份发送邮件。第一种:把自己当作outlook之类的客户端,先连到发信服务器,提交邮件后让发件服务器往外发送。第二种:把自己当作发信服务器,直接通过smtp连接收件人的服务器发送邮件。
这里我不推荐第二种方式,原因是:如果你php所在服务器的域名,ip,mx记录没有严格设置好的话,一般收件服务器有很大的几率会拒收;发送邮件本身的传输过程时间无法控制,如果和收件服务器有很大的延时,会严重影响自己的web服务器的工作,另外也不具有失败重发等处理。
对于发送邮件,windows和unix和很大的差别。windows一般来说都是像outlook那样的方式,用smtp协议连到发件服务器发送邮件。unix有自己的传统方式,就是unix主机自带 smtp server,传统的就是sendmail。另外还有个“sendmail”的概念,这里说的是一个程序的名字,无论是sendmail,qmail,postfix等等,都提供这个命令程序,通过它,可以把邮件放入本地邮件发送队列,让sendmail,qmail,postfix之类的投递程序去投递发送。sendmail程序一般是从标准输入里读入邮件内容。php的mail()函数实际上会打开sendmail程序,通过标准输入把邮件内容传给它,由sendmail程序来发送,剩下的就不管了。
所以大家可以看到,php里关于mail() 这个函数的说明,如果是在windows上,一般是设置 php.ini里 SMTP 和 smtp_port 选项的值,通过类outlook客户端的方式发送,但是这种方式的致命弱点是不支持smtp验证,而现在邮件服务器基本都是需要smtp验证的。uxni下一般需要设置 sendmail_path ,来说明sendmail程序的路径。当然windows上也可以用sendmail程序发送。
如果是unix,最理想的情况是,你的php所在的web服务器本身也是个smtp server,并设置好了mx记录等等,或者你有个能发送邮件的sendmail程序(自己写,封装smtp发送)那么先配置好 php.ini 里的sendmail_path,通过mail()函数就直接发送了。
如果没有能用的sendmail程序,那么就要通过socket 用smtp协议发送了,php这方面有很多扩展的库,可以直接拿来用。建议连上一个服务器让他帮你发,不建议直接连收件服务器(原因前面说了)。这里还有就是不建议直接在网页上php里连接发送,推荐的方式是把邮件写到数据库或文件里,让另一个程序(php,perl,python 都可以写)扫描后通过sokcet连接发送。这样既给用户有了好的响应体验,也可以控制发送的过程。

What’s still popular is the ease of use, flexibility and a strong ecosystem. 1) Ease of use and simple syntax make it the first choice for beginners. 2) Closely integrated with web development, excellent interaction with HTTP requests and database. 3) The huge ecosystem provides a wealth of tools and libraries. 4) Active community and open source nature adapts them to new needs and technology trends.

PHP and Python are both high-level programming languages that are widely used in web development, data processing and automation tasks. 1.PHP is often used to build dynamic websites and content management systems, while Python is often used to build web frameworks and data science. 2.PHP uses echo to output content, Python uses print. 3. Both support object-oriented programming, but the syntax and keywords are different. 4. PHP supports weak type conversion, while Python is more stringent. 5. PHP performance optimization includes using OPcache and asynchronous programming, while Python uses cProfile and asynchronous programming.

PHP is mainly procedural programming, but also supports object-oriented programming (OOP); Python supports a variety of paradigms, including OOP, functional and procedural programming. PHP is suitable for web development, and Python is suitable for a variety of applications such as data analysis and machine learning.

PHP originated in 1994 and was developed by RasmusLerdorf. It was originally used to track website visitors and gradually evolved into a server-side scripting language and was widely used in web development. Python was developed by Guidovan Rossum in the late 1980s and was first released in 1991. It emphasizes code readability and simplicity, and is suitable for scientific computing, data analysis and other fields.

PHP is suitable for web development and rapid prototyping, and Python is suitable for data science and machine learning. 1.PHP is used for dynamic web development, with simple syntax and suitable for rapid development. 2. Python has concise syntax, is suitable for multiple fields, and has a strong library ecosystem.

PHP remains important in the modernization process because it supports a large number of websites and applications and adapts to development needs through frameworks. 1.PHP7 improves performance and introduces new features. 2. Modern frameworks such as Laravel, Symfony and CodeIgniter simplify development and improve code quality. 3. Performance optimization and best practices further improve application efficiency.

PHPhassignificantlyimpactedwebdevelopmentandextendsbeyondit.1)ItpowersmajorplatformslikeWordPressandexcelsindatabaseinteractions.2)PHP'sadaptabilityallowsittoscaleforlargeapplicationsusingframeworkslikeLaravel.3)Beyondweb,PHPisusedincommand-linescrip

PHP type prompts to improve code quality and readability. 1) Scalar type tips: Since PHP7.0, basic data types are allowed to be specified in function parameters, such as int, float, etc. 2) Return type prompt: Ensure the consistency of the function return value type. 3) Union type prompt: Since PHP8.0, multiple types are allowed to be specified in function parameters or return values. 4) Nullable type prompt: Allows to include null values and handle functions that may return null values.


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