从符合正则表达式到今天的复杂工具，电子邮件验证已经经历了几个不同的时代。在研究验证技术和最佳实践的历史之前，了解基础知识是至关重要的。

什么是电子邮件验证，为什么它很重要？

电子邮件验证是一种验证收件人的地址是否存在并接受邮件的方法。一些技术通过确认该地址属于预定的人，并且收件人希望收到此类通信，从而使验证多了一个步骤。在这个过程中，你将从你的名单中消除有风险和无效的地址，并保护你作为一个有信誉的发件人在互联网服务提供商（ISP）的名字。

在发送营销和交易信息之前，注意验证用户的电子邮件，也会增加您的信息直接到达读者inbox 的机会。此外，营销活动的指标更加准确，并为未来的数据驱动决策提供更深入的见解。

很久以前，在一个很远很远的时代......它开始于语法验证

Checking an email address for syntax accuracy has been the simplest version of email validation. ǞǞǞ core elements of a valid email address are the local part, the @ symbol, the domain, and finally, the extension (.com, .org, etc.). To help standardize all the various syntaxes, specifications called Requests For Comments (RFCs) were published to determine what characters would be acceptable for local and domain parts. These RFCs eventually became quite extensive and created the need for open-source libraries to help validate email syntax in many languages.

语法验证的另一个重要组成部分是明显的拼写错误，如heyitsme@gmsil.com。针对这些类型的错误对你现有的列表进行校对仍然是一种最佳做法。

验证SMTP命令和垃圾邮件的攻击

认识到在验证电子邮件地址方面需要帮助，互联网服务提供商（ISP）开始建立电子邮件地址验证功能。因此，"VRFY"（也被称为验证）被作为一个SMTP命令建立起来，使发件人能够询问接收邮件服务器一个电子邮件地址是否有效。由于希望利用VRFY为银河系的互联网带来和平和秩序，它很快就落入了黑暗势力的手中；垃圾邮件发送者。在这一功能被大规模滥用后，ISP管理员禁用了VRFY，使电子邮件地址验证处于混乱状态。

SMTP Ping (垃圾邮件的威胁)

在VRFY倒下之后，发送者创造性地设计了SMTP Ping，这是一种不同的方法来验证一个电子邮件地址是否有效。SMTP Ping被用来检查远程邮件服务器，看一个电子邮件地址是否有效。与互联网服务提供商（ISP）的远程邮件服务器（如Gmail）的连接会像实际发送邮件一样，但在没有实际发送邮件的情况下突然中断。

通常情况下，在发送邮件服务器和接收ISP邮件服务器之间的连接中进行的对话看起来是这样的。

在某些情况下，ISP可以提供这样的反馈。

有了SMTP Ping，发件人在请求向指定的电子邮件地址发送邮件后，在看到ISP的回复后，可以缩短对话时间。这成为一种对ISP进行ping的方式，以了解接收邮件服务器是否发现电子邮件地址有效或无效，并有一定程度的信心。

SMTP Ping的黑暗面

ISPs consider SMTP Ping — also known as the broken handshake — as spammer behavior. ISPs can easily tell that you’re just checking validity of email addresses by looking 在 conversation patterns: Calling in and hanging up repetitiously, with no (or very little) messages actually being sent, ends up in their mail server logs. After the history with SMTP VRFY, this type of behavior is now known to be spammy. ISPs are cracking down on this behavior and cracking down hard. Microsoft for example, considers this type of practice to be malicious and Hotmail finds SMTP Ping as evidence of a directory harvest attack. SMTP Ping attempts in progress will typically drop a hard block on all connections from the sending IP address. ISPs dislike SMTP Ping, and so do blacklist operators. Keep it up, and you’ll almost surely end up getting blacklisted.

此外，许多ISP将收件人验证推迟到服务器对话结束后，导致在没有确认电子邮件地址有效性的情况下接受邮件--这是一个假阳性。一些ISP还用灰名单来保护收件人。在灰名单协议下，接收服务器会拒绝来自未知发件人的电子邮件。因此，即使是有效的电子邮件地址，SMTP Pings也会返回一个错误信息--假性否定。

长话短说，这是一个非常糟糕的做法，而且不可靠。

愿验证与你同在--电子邮件验证的最佳实践

你可以采取各种步骤来确保你验证电子邮件的方法是强大的，包括。

• 主动处理错别字。 Consider adding an auto-complete tool to your email entry field with popular @example.com extensions, such as @gmail.com. Allowing users to select from the preformatted entries reduces the potential for a typo.

• 追求双重选择。 Sending an email confirming a user request that requires them to verify their email satisfies regulations for certain markets and provides validation.

• 利用技术优势。 Various email verification tools offer an easy, affordable way to maximize communication potential and maintain friendly relationships with ISPs.

• 建立一个常规。 While it may be tempting to validate emails only when executing a bulk-send campaign, regularly scheduling a validation may be the better option. Consider how often and from where emails join your list — the more options for capturing contact information, the more potential for invalid addresses.

Why Use Email Validation Tools?

使用电子邮件验证工具（EV）的原因有很多，包括。

• 它为你节省了时间。 EVs rely on automated processes for validation that reduce the time associated with manual look-ups.

• 它为你省钱。 A clean email list with valid addresses eliminates bounces and increases ROI by reducing unnecessary spending.

• 它使你不被列入封锁名单。 Using EVs lowers spam complaints that can lead to message and sender blocking.

• 它提高了交付能力。 Readers need to receive your emails before interacting with them, so deliverability is a priority for promotional and transactional communications.

• 它提供实时结果。 Being able to validate immediately across different points of the buyer’s process supplies you with higher-quality contact information.

一个新的希望：数据驱动

Rather than rely on SMTP Ping, there’s a different data-driven approach that does not make enemies with ISPs. Validating email addresses can be done by looking up against a large data set, with event data including hard bounces, deliveries, and engagement, as well as incorporating syntax validation, typo detection, DNS queries for valid domains, and quality checks for free, role-based, and disposable email addresses.  This method heavily relies on the depth and breadth of the data the email validation tool or service is built upon, instead of depending on the ISP to provide back a specific response. You may not want to judge Master Yoda based on his size, but you’ll want to judge an email address validation tool by its data size.

SparkPost’s 收件人验证 is built on top of its large email data footprint, sending more than 37% of the world’s B2C and B2B email. Our data science team has done a thorough analysis of billions of email bounces and delivery events. Our findings establish that a single hard bounce isn’t enough to establish you shouldn’t send to an address. Using our data footprint, we are constantly updating our list of recipients and our algorithms to capture the true validity of a hard bounce, and analyzing all related email events to best answer the question: Can you deliver to this given email address?

As we continue to build and iterate upon our 收件人验证, our goal is to make ours the most dependable and fastest validation tool on the market. Rumor has it our Recipient Validation will be able to make the Kessel Run in less than 12 parsecs, or at least something along those lines…