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> ...@(valid)example.org(honest) Are those parens really permitted in the host name? I'm looking at RFC 3696. > 3. Restrictions on email addresses > .... T

> ...@(valid)example.org(honest) Are those parens really permitted in the host name? I'm looking at RFC 3696. > 3. Restrictions on email addresses > .... The syntax of the domain part corresponds to that in the previous section. and > 2. Restrictions on domain (DNS) names > Any characters, or combination of bits (as octets), are permitted in DNS names. However, there is a preferred form that is required by most applications. This preferred form has been the only one permitted in the names of top-level domains, or TLDs. .... The LDH rule, as updated, provides that the labels (words or strings separated by periods) that make up a domain name must consist of only the ASCII [ASCII] alphabetic and numeric characters, plus the hyphen. No other symbols or punctuation characters are permitted, nor is blank space. https://tools.ietf.org/html/rfc3696#section-2 https://tools.ietf.org/html/rfc3696#section-2

wtbob 10y ago
> > ...@(valid)example.org(honest) > Are those parens really permitted in the host name? I'm looking at RFC 3696. RFC5322 states that an addr-spec consists of a local-part, followed by @, followed by a domain. It states that a domain may be a domain-literal; a domain-literal may begin and end with commented folding whitespace (CFWS). It's all in https://tools.ietf.org/html/rfc5322#section-3.4.1 https://tools.ietf.org/html/rfc5322#section-3.4.1 It's only the dtext portion of the domain-literal which must consist of printable ASCII characters, not including [, ] or \. Yes, foo@bar!baz!quux is a valid RFC5322 email address (decimal 33, i.e. !) is allowed, per the dtext production of the spec) — and so is foo@(comment (nested comment (escaped \(comment)))bar!baz!quux(another (comment (to prove) the point)) Whether one should ever actually use such an address is, of course, another matter entirely.
- tedmiston 10y ago
  Thank you for that; this has been eyeopening. The possibility of having a valid email address where the second-level domain component can't actually be registered as a domain, to the best of my understanding, eg "bar!.com", is interesting.
  - wtbob 10y ago
    > The possibility of having a valid email address where the second-level domain component can't actually be registered as a domain, to the best of my understanding, eg "bar!.com", is interesting. It is! Conceivably, it could be used to implement a new kind of domain-less mail system, e.g. foo@$megamail or something.

wtbob 10y ago

> > ...@(valid)example.org(honest) > Are those parens really permitted in the host name? I'm looking at RFC 3696. RFC5322 states that an addr-spec consists of a local-part, followed by @, followed by a domain. It states that a domain may be a domain-literal; a domain-literal may begin and end with commented folding whitespace (CFWS). It's all in https://tools.ietf.org/html/rfc5322#section-3.4.1 https://tools.ietf.org/html/rfc5322#section-3.4.1 It's only the dtext portion of the domain-literal which must consist of printable ASCII characters, not including [, ] or \. Yes, foo@bar!baz!quux is a valid RFC5322 email address (decimal 33, i.e. !) is allowed, per the dtext production of the spec) — and so is foo@(comment (nested comment (escaped \(comment)))bar!baz!quux(another (comment (to prove) the point)) Whether one should ever actually use such an address is, of course, another matter entirely.

tedmiston 10y ago
Thank you for that; this has been eyeopening. The possibility of having a valid email address where the second-level domain component can't actually be registered as a domain, to the best of my understanding, eg "bar!.com", is interesting.
- wtbob 10y ago
  > The possibility of having a valid email address where the second-level domain component can't actually be registered as a domain, to the best of my understanding, eg "bar!.com", is interesting. It is! Conceivably, it could be used to implement a new kind of domain-less mail system, e.g. foo@$megamail or something.