无点域名
Dotless Domains

原始链接: https://lab.avl.la/dotless/

无点域名,例如“http://com/”这样的单标签域名,是顶级域名(TLD),可以通过TLD顶点的A/AAAA或MX记录直接访问其web或邮件服务。ICANN不鼓励在通用顶级域名(gTLD)上采用这种做法,但国家代码顶级域名(ccTLD)有时由于司法管辖权的不同而允许这样做。向无点域名发送电子邮件是有问题的;SMTP通常需要两个标签(domain.tld)。 该文档列出了当前和历史上具有顶点A/AAAA记录(用于web访问)和MX记录(用于电子邮件)的ccTLD示例。一些ccTLD,例如.cf和.gp,目前只有MX记录,理论上允许接收电子邮件。ICANN曾短暂要求新注册的TLD在注册后必须具有顶点DNS记录。 最后,该文档幽默地探讨了使用DNS根域(.)的“无点点”的理论可能性,并指出其极不可能实现。

这个Hacker News帖子讨论了“无点域名”,特别是没有传统顶级域名(如`.com`)的域名的有效性和技术方面。一位评论者提到浏览器可以将十进制IP地址解释为URL。另一位询问将IP地址转换为十进制形式的算法。 讨论随后转向电子邮件验证。一位用户在研究表明像“a@b”这样的邮件在“b”是一个具有MX记录的单字母顶级域名时可能是有效的之后,创建了一个非常基本的正则表达式用于电子邮件验证(`/^.{1,}@.{1,}$/`)。其他评论者讨论了这是否有效,并建议使用RFC中提到的用于验证电子邮件地址的标准正则表达式。另一位用户询问电子邮件验证的目的,最初的用户回答是为了在发送电子邮件之前进行基本的错误预防。

原文

The term "dotless domain" usually refers to top-level domains (TLDs) – think com, gov, etc – that are reachable themselves using a web browser or email server.

That is, they are working domains that consist of a single label: http://com/, as opposed to http://example.com/; or contact@gov, as opposed to [email protected]. This can happen if the domain's DNS zone contains A/AAAA or MX records in its apex.[1]

Both the ICANN and the IAB are notoriously against the practice,[1][2] so ICANN prohibits it where it can – namely, on gTLDs.[3] However, ccTLDs (country code TLDs) fall largely under their own country's jurisdiction! As such, there currently are and historically have been examples of active dotless ccTLDs.

For email, the protocol itself would need to allow a dotless domain as a destination address. According to ICANN's SSAC,[1] SMTP requires at least two labels (i.e. domain.tld) to deliver an email, so it is unlikely Mauritania would receive an email sent to contact@mr, for example. For completeness' sake, however, apex MX servers are listed below as well.

Table of Contents:

  1. A or AAAA
    1. Current
      1. Screenshots
    2. New TLDs
    3. Historical
      1. Screenshots
  2. MX only
    1. Current
    2. Historical
  3. Bonus: Dotless Dot?
  4. Special Thanks
  5. References

# A or AAAA

# Current

These are TLDs that, as of the last check, contain apex A or AAAA records. Many have had those records since the IETF compiled a list in 2013;[5] other dates indicate an observation by me, directly.

Last checked: 31 Mar. 2025.

# Screenshots

# New TLDs

In order to prevent local aliases from colliding with newly registered TLDs (think programmers using foo.bar as a test domain before the creation of the gTLD .bar), ICANN published a resolution in 2014 requiring new TLDs to include a few apex DNS records on their TLDs for at least 90 days.[4]

As of the last check, no TLDs had informational apex records. This is what they usually look like:

Last checked: 31 Mar. 2025.

# Historical

These are TLDs that previously had apex records, but no longer do so. Much of it comes from a list compiled by the IETF in 2013;[5] other dates indicate an observation by me, directly.

# Screenshots


# MX only

# Current

These are TLDs that, as of the last check, contain only MX apex records; that is, they could, in theory, send and receive email, but have no reachable website. Many have had those records since the IETF compiled a list in 2013;[5] other dates indicate an observation by me, directly.

Territory ccTLD Email server
(MX)
First seen on
Central African Republic .cf mail.intnet.cf 2013
Guadeloupe (FR) .gp ns1.nic.gp 2013
Guatemala .gt aspmx2.googlemail.com
aspmx4.googlemail.com
aspmx5.googlemail.com
aspmx.l.google.com
alt1.aspmx.l.google.com
alt2.aspmx.l.google.com
2013
Croatia .hr alpha.carnet.hr 2013
Comoros .km mail1.comorestelecom.km 2013
Martinique (FR) .mq mx1-mq.mediaserv.net 2013
Mauritania .mr mail.nic.mr Aug. 2021
Trinidad and Tobago .tt aspmx.l.google.com
alt1.aspmx.l.google.com
2013
Ukraine .ua mr.kolo.net 2013

Last checked: 31 Mar. 2025.

# Historical

Similarly to the historical A/AAAA records, these are TLDs that previously (only) had apex MX records, but no longer do so. Many come from a list compiled by the IETF in 2013;[5] other dates indicate an observation by me, directly.

Territory ccTLD Email server
(MX)
Known
working date
Åland Islands (FI) .ax mail.aland.net 2013
Dominica .dm mail.nic.dm 2013
Cambodia .kh ns1.dns.net.kh Jan. 2022—
Oct. 2022
Sri Lanka .lk malithi-slt.nic.lk
malithi-lc.nic.lk
2013—
Jan. 2024
Panama .pa ns.pa 2013—
Jan. 2024
Philippines .ph mx1.sendnow.ph
mx2.sendnow.ph
mx3.sendnow.ph
mx4.sendnow.ph
mx5.sendnow.ph
Aug. 2021—
Oct. 2022
Suriname .sr spsbbank.sr Aug. 2021—
Jan. 2024
Vatican .va raphaelmx1.posta.va
raphaelmx2.posta.va
raphaelmx3.posta.va
2013
Yemen .ye mail.yemen.net.ye 2013

# Bonus: Dotless Dot?

Dotless domains work because top-level domains (TLDs) are just as much nodes in the DNS tree as second-level domains (SLDs), or any other level beneath them. That means there is no technicaly limitation to their DNS records, and they may contain A, AAAA and MX records.

Another, often forgotten node in the DNS tree is the root, represented by a single dot, .. It's the parent of all TLDs! Though it's usually omitted, every domain terminates with a dot: example.com is, in fact, example.com.; example is a child of com which, in turn, is a child of ..

Followed to its logical conclusion, this means the root domain could also contain A, AAAA and MX records! That is, accessing http://./ or emailing example@. is, at least in theory, possible.

Sadly, the odds of that ever happening are very nearly zero. The root doesn't have A, AAAA or MX records and likely won't, ever.

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