feat(mailer-smtp): add SCRAM-SHA-256 auth, Ed25519 DKIM, opportunistic TLS, SNI cert selection, pipelining and delivery/bridge improvements

rust/crates/mailer-smtp/src/client/config.rs

@@ -37,6 +37,12 @@ pub struct SmtpClientConfig {
     /// Maximum connections per pool. Default: 10.
     #[serde(default = "default_max_pool_connections")]
     pub max_pool_connections: usize,
+
+    /// Accept invalid TLS certificates (expired, self-signed, wrong hostname).
+    /// Standard for MTA-to-MTA opportunistic TLS per RFC 7435.
+    /// Default: false.
+    #[serde(default)]
+    pub tls_opportunistic: bool,
 }
 
 /// Authentication configuration.
@@ -60,8 +66,15 @@ pub struct DkimSignConfig {
     pub domain: String,
     /// DKIM selector (e.g. "default" or "mta").
     pub selector: String,
-    /// PEM-encoded RSA private key.
+    /// PEM-encoded private key (RSA or Ed25519 PKCS#8).
     pub private_key: String,
+    /// Key type: "rsa" (default) or "ed25519".
+    #[serde(default = "default_key_type")]
+    pub key_type: String,
+}
+
+fn default_key_type() -> String {
+    "rsa".to_string()
 }
 
 impl SmtpClientConfig {