We have recently published an hosted email validation service based on our EmailVerify.NET, an award-winning and well known email validation component for the .NET platform; while I can't answer for every other service you mentioned, I can certainly do it for ours:
EmailVerify.NET does not employ the VRFY command at all, as it may lead to potential bans from external mail exchangers;
blacklisting is always possible and Netiquette must always be respected while performing the validation job (although there are no written rules here): our component allows to bind itself to any available IP address and to cycle the originating IP addresses during the validation process, thus increasing the number of validations that can be performed at once while lowering at the same time the possibility of a ban.
My experience also shows that most email validation services out there do not offer the quality one would expect for even syntax validation (there are at least 7 different RFCs to follow, a simple regular expression is not the right choice here); before choosing one, I suggest you to ask for a demo with your own sample data (EmailVerify.NET has an online demo page you can play with, if you wish). Most, for example, do not support quoted words or non-ASCII domains or mailboxes, which are becoming quite common nowadays, or do not filter out disposable (temporary) email addresses.
The Paid Email verification service providers typically check below points to verify an email address.
Email Address Syntax Check
Domain/MX Records Check
Role-Based Account Detection
Disposable Email Address (DEA) Detection
Honeypot/ Spam Trap Detection
Checking DNSBLs and URI DNSBLs for blacklisting
Though all of them does not check everything mentioned above but it is best practice to choose a provider who checks all of the above. You can test service and results of some of the best providers from here.
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我们最近基于我们的 EmailVerify.NET，一个屡获殊荣且众所周知的 .NET 平台电子邮件验证组件；虽然我无法回答您提到的所有其他服务，但我当然可以为我们的服务做到这一点：
我的经验还表明，大多数电子邮件验证服务都无法提供人们所期望的语法验证质量（至少有 7 个不同的 RFC 需要遵循，简单的正则表达式在这里不是正确的选择）；在选择一个之前，我建议您索取带有您自己的示例数据的演示（EmailVerify.NET 有一个 如果您愿意，您可以使用在线演示页面）。例如，大多数不支持引用的单词或非 ASCII 域或邮箱（这些现在变得相当普遍），或者不过滤掉一次性（临时）电子邮件地址。
We have recently published an hosted email validation service based on our EmailVerify.NET, an award-winning and well known email validation component for the .NET platform; while I can't answer for every other service you mentioned, I can certainly do it for ours:
My experience also shows that most email validation services out there do not offer the quality one would expect for even syntax validation (there are at least 7 different RFCs to follow, a simple regular expression is not the right choice here); before choosing one, I suggest you to ask for a demo with your own sample data (EmailVerify.NET has an online demo page you can play with, if you wish). Most, for example, do not support quoted words or non-ASCII domains or mailboxes, which are becoming quite common nowadays, or do not filter out disposable (temporary) email addresses.
付费电子邮件验证服务提供商通常会检查以下几点来验证电子邮件地址。
虽然所有这些都不会检查上述所有内容，但最佳做法是选择检查上述所有内容的提供商。您可以从 测试一些最佳提供商的服务和结果在这里。
The Paid Email verification service providers typically check below points to verify an email address.
Though all of them does not check everything mentioned above but it is best practice to choose a provider who checks all of the above. You can test service and results of some of the best providers from here.