EmailCheck / Questions问题页 / Does an email verification API check whether the actual mailbox exists?
Does an email verification API check whether the actual mailbox exists?邮箱验证 API 会检查具体邮箱到底存不存在吗？
EmailCheck does not — and it is worth knowing exactly what it does instead. It checks the domain: MX routing, domain age from registration records, disposable / role / free-provider signals, and likely typos with a correction. Mailbox-level probing over SMTP is rejected or greylisted by major providers, which is why any API “guaranteeing” that a mailbox exists is overselling what the protocol allows.
EmailCheck 不查——而且值得你弄清它到底查什么。它查域名：MX 路由、来自注册记录的域名年龄、一次性/角色/免费服务商信号、疑似拼写错误及纠正建议。走 SMTP 的邮箱级探测会被主流服务商拒绝或灰名单处理，所以任何「保证邮箱存在」的 API，都是在超出协议允许的范围过度承诺。
What “mailbox exists” would actually require「邮箱存在」到底需要什么
To ask a mail server whether one specific mailbox exists, a verifier has to open an SMTP conversation and start a delivery (an RCPT TO probe), then stop before sending. Two decades of spam abuse have trained providers to defeat exactly this: servers greylist unknown senders, tarpit probes, return deliberately vague answers, or accept everything (catch-all) and sort it out later. The result is that a “mailbox check” is often a guess wearing a lab coat — and on catch-all domains it is provably meaningless, since the server accepts every address by design.
That is why EmailCheck's position is printed in every response rather than buried in a FAQ: domain-level only, no SMTP probing, a valid result does not confirm the mailbox exists.
想问一台邮件服务器某个具体邮箱存不存在，验证方得打开一次 SMTP 会话、发起投递（RCPT TO 探测），再在真发送前停住。二十年的垃圾邮件攻防已经把服务商训练得专门防这一手：灰名单陌生发件人、给探测连接降速、返回刻意含糊的答案，或者干脆全收（catch-all）事后再说。结果是，「邮箱检查」常常是穿着实验服的猜测——在 catch-all 域名上更是可证地无意义，因为那台服务器按设计接受一切地址。
所以 EmailCheck 的立场印在每个响应里，而不是埋在某个 FAQ 里：只做域名级、不做 SMTP 探测、valid 结果不确认邮箱存在。
What domain-level checks catch instead域名级检查能抓住什么
Most addresses that hurt you fail at domain level long before mailbox existence matters:
- Typos — gmial.com, hotmial.com: syntactically fine, and the reason confirmation mail vanishes. EmailCheck returns
typoLikelyplus asuggestion. - Dead or parked domains — no MX records, or a domain that no longer routes mail.
- Disposable domains — throwaway inboxes used to pass a signup gate, flagged per address.
- Role accounts — postmaster@, admin@ and friends: real, but rarely the audience you meant to mail.
- Brand-new domains —
domainAgeDaysfrom RDAP registration records (null when there is no record — never estimated), a useful fraud and quality signal.
真正会坑到你的地址，绝大多数在域名层就露馅了，根本轮不到邮箱存在与否：
- 拼写错误——gmial.com、hotmial.com：格式完全合法，确认邮件却石沉大海。EmailCheck 返回
typoLikely和suggestion。 - 死域名/停放域名——没有 MX 记录，或域名已经不收信。
- 一次性域名——用来过注册门槛的临时收件箱，逐条标记。
- 角色账号——postmaster@、admin@ 之类：是真的，但很少是你想发信的对象。
- 刚注册的域名——
domainAgeDays来自 RDAP 注册记录（无记录返 null，从不估算），是好用的欺诈与质量信号。
Try it on a real address拿真实地址试一下
Live call to the production API — the same check described on this page.
实时调生产 API——就是本页说的这个检查。
Scope, stated plainly: EmailCheck checks domains, not mailboxes — no SMTP probing, no claim that a specific mailbox exists. Every API response carries scope: "domain-level" and a note saying exactly what was checked.
范围说死：EmailCheck 查的是域名，不是邮箱——不做 SMTP 探测，不声称某个具体邮箱存在。每个 API 响应都带 scope: "domain-level" 和一段说明，把查过的范围写清。