--- /dev/null
+Email length
+------------
+http://tools.ietf.org/html/rfc5321#section-4.1.2
+ Forward-path = Path
+
+ Path = "<" [ A-d-l ":" ] Mailbox ">"
+
+http://tools.ietf.org/html/rfc5321#section-4.5.3.1.3
+http://tools.ietf.org/html/rfc1035#section-2.3.4
+
+DNS
+---
+
+http://tools.ietf.org/html/rfc5321#section-2.3.5
+ Names that can
+ be resolved to MX RRs or address (i.e., A or AAAA) RRs (as discussed
+ in Section 5) are permitted, as are CNAME RRs whose targets can be
+ resolved, in turn, to MX or address RRs.
+
+http://tools.ietf.org/html/rfc5321#section-5.1
+ The lookup first attempts to locate an MX record associated with the
+ name. If a CNAME record is found, the resulting name is processed as
+ if it were the initial name. ... If an empty list of MXs is returned,
+ the address is treated as if it was associated with an implicit MX
+ RR, with a preference of 0, pointing to that host.
+
+is_email() author's note: We will regard the existence of a CNAME to be
+sufficient evidence of the domain's existence. For performance reasons
+we will not repeat the DNS lookup for the CNAME's target, but we will
+raise a warning because we didn't immediately find an MX record.
+
+Check for TLD addresses
+-----------------------
+TLD addresses are specifically allowed in RFC 5321 but they are
+unusual to say the least. We will allocate a separate
+status to these addresses on the basis that they are more likely
+to be typos than genuine addresses (unless we've already
+established that the domain does have an MX record)
+
+http://tools.ietf.org/html/rfc5321#section-2.3.5
+ In the case
+ of a top-level domain used by itself in an email address, a single
+ string is used without any dots. This makes the requirement,
+ described in more detail below, that only fully-qualified domain
+ names appear in SMTP transactions on the public Internet,
+ particularly important where top-level domains are involved.
+
+TLD format
+----------
+The format of TLDs has changed a number of times. The standards
+used by IANA have been largely ignored by ICANN, leading to
+confusion over the standards being followed. These are not defined
+anywhere, except as a general component of a DNS host name (a label).
+However, this could potentially lead to 123.123.123.123 being a
+valid DNS name (rather than an IP address) and thereby creating
+an ambiguity. The most authoritative statement on TLD formats that
+the author can find is in a (rejected!) erratum to RFC 1123
+submitted by John Klensin, the author of RFC 5321:
+
+http://www.rfc-editor.org/errata_search.php?rfc=1123&eid=1353
+ However, a valid host name can never have the dotted-decimal
+ form #.#.#.#, since this change does not permit the highest-level
+ component label to start with a digit even if it is not all-numeric.
+
+Comments
+--------
+Comments at the start of the domain are deprecated in the text
+Comments at the start of a subdomain are obs-domain
+(http://tools.ietf.org/html/rfc5322#section-3.4.1)
projects / yaffs-website / blobdiff