Enum AddressLiteral 

pub enum AddressLiteral {
    Reject,
    Routable,
    Rfc5321,
}

Which address-literal spellings the domain may take (RFC 5321 §4.1.3).

The grammar names three alternatives:

address-literal = "[" ( IPv4-address-literal /
                        IPv6-address-literal /
                        General-address-literal ) "]"

A domain literal is refused unless asked for, so the default is Reject. Of the two readings a caller can opt into, the destination-oriented one, Routable, covers the first two alternatives, which are the only ones mail can be delivered to. A reader of an identity rather than a destination needs the third: an X.509 rfc822Name is a Mailbox as RFC 5321 defines it (RFC 5280 §4.2.1.6), and refusing a spelling the grammar names makes the certificate carrying it unreadable rather than merely unroutable.

Variants

Reject

Reject every [...] domain literal.

Routable

Accept only a literal naming a routable destination: an IPv4 dotted-quad or an IPv6:-tagged IPv6 address.

Stricter than the grammar in one place, deliberately: RFC 5321 Snum is 1*3DIGIT in the range 0..=255 with no rule against padding, so [012.0.2.1] is inside the grammar. It is rejected here because a zero-padded octet is read as octal by some resolvers, and a destination that resolves two ways is not one. Use Rfc5321 to read the grammar as written.

Rfc5321

Accept every alternative the grammar names, General-address-literal included, so postmaster@[AS400:QSYS] parses.

General-address-literal = Standardized-tag ":" 1*dcontent
Standardized-tag        = Ldh-str
dcontent                = %d33-90 / %d94-126

The IPv6 tag keeps its own alternative’s meaning: RFC 5321 §4.1.3 requires a standardized tag to be defined by a Standards-Track RFC, and IPv6 is, so [IPv6:...] must still hold an IPv6 address and is not reinterpreted as free dcontent.

Trait Implementations

impl Clone for AddressLiteral

fn clone(&self) -> AddressLiteral

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for AddressLiteral

impl Debug for AddressLiteral

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for AddressLiteral

fn default() -> AddressLiteral

Returns the “default value” for a type.

impl Eq for AddressLiteral

impl PartialEq for AddressLiteral

fn eq(&self, other: &AddressLiteral) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for AddressLiteral