Enum AuthMechanism 

#[non_exhaustive]
pub enum AuthMechanism {
    Plain,
    Login,
    XOAuth2,
    OAuthBearer,
    ScramSha256,
}

SASL authentication mechanisms supported by this client.

Today the crate implements PLAIN (RFC 4616) and LOGIN (the historical mechanism used by many submission servers). The enum is non_exhaustive so that future additions (e.g. XOAUTH2, SCRAM-SHA-256) do not require a major version bump.

PLAIN is preferred when both are advertised: it is one network round-trip rather than two, and is an IETF-standard SASL mechanism. LOGIN is retained for compatibility with older submission servers that advertise only it.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Plain

SASL PLAIN (RFC 4616). Sends \0user\0pass base64-encoded as the initial response, completing in a single round-trip.

Login

LOGIN. Sends username and password as separate base64 lines in response to two 334 server prompts.

XOAuth2

SASL XOAUTH2 (Google / Microsoft OAuth 2.0 SMTP extension). Sends user={user}\x01auth=Bearer {token}\x01\x01 base64-encoded as the initial response. The “credential” passed to login_with for this mechanism is an OAuth 2.0 access token, not a static password — auto-selection by login() deliberately does NOT pick this mechanism for that reason.

OAuthBearer

SASL OAUTHBEARER (RFC 7628). The IETF-standard OAuth 2.0 SASL mechanism. Sends n,a={user},\x01auth=Bearer {token}\x01\x01 (GS2 header + Bearer token) base64-encoded as the initial response. More interoperable than XOAUTH2 and defined by an IETF RFC. Like XOAUTH2, auto-selection by login() does NOT pick this mechanism because the credential is a token, not a password.

Available only with the oauthbearer cargo feature (default-on).

ScramSha256

SASL SCRAM-SHA-256 (RFC 5802 / RFC 7677). Challenge-response authentication: the client never transmits the password, and the server proves possession of the salted hash through a signature step. Auto-selection by login() prefers this mechanism over PLAIN and LOGIN when the server advertises it.

Available only with the scram-sha-256 cargo feature (default-on).

Implementations

impl AuthMechanism

pub const fn name(self) -> &'static str

SMTP-on-the-wire keyword for this mechanism.

Trait Implementations

impl Clone for AuthMechanism

fn clone(&self) -> AuthMechanism

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for AuthMechanism

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

Formats the value using the given formatter.

impl Display for AuthMechanism

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

Formats the value using the given formatter.

impl Hash for AuthMechanism

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for AuthMechanism

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for AuthMechanism

impl Eq for AuthMechanism

impl StructuralPartialEq for AuthMechanism