All this stuff brings up a very interesting point about deliverable email
addresses in draft-seantek-mail-regexen:
What are the domain part limitations on deliverable email addresses, that are
not encapsulated by the RFC 5321 ABNF?
The domain production is limited to 253 characters. I am sure of this.
Each sub-domain production is limited to 63 characters. I am also sure of this.
I strongly believe that domain productions cannot be parseable IPv4 addresses.
(Note: they can never be parseable as IPv6 addresses, as that would require :
which is not part of a domain production.)
The string “18.104.22.168” is a valid domain production. However, it is not (or
*should not*) be considered a deliverable email address, because when passed to
the famous function “gethostbyname”, that function will certainly return
22.214.171.124; it will not perform a lookup of the domain record with a top-level
label of “4”. This is also supported by RFC 1912: “Labels may not be all
numbers”. But an individual label can be a number, such as “411.org”.
I have tried “email@example.com” -- Windows and Unix/Linux stacks will try to query
the DNS for that string and not parse it as IPv4. So, it is syntactically a
valid, deliverable email address. But foo@411 will get IPv4-parsed to
0.0.1.155, which means that “411” should not be considered a valid domain name
for a deliverable email address.
True? Are there other limitations?
ietf-smtp mailing list