feat(starttls): remove opportunistic value

This commit removes the `Opportunistic` value from the struct `StartTls`.
This value was strictly equivalent to `Always` and could potentially
cause confusion.

README.md

@@ -321,7 +321,7 @@ backend/
 
 The contact form supports multiple SMTP configurations:
 - **Implicit TLS (SMTPS)** - typically port 465
-- **STARTTLS (Always/Opportunistic)** - typically port 587
+- **STARTTLS (Always)** - typically port 587
 - **Unencrypted** (for local dev) - with or without authentication
 
 The `SmtpTransport` is built dynamically from `EmailSettings` based on

src/route/contact/mod.rs

@@ -62,7 +62,7 @@ impl TryFrom<&EmailSettings> for SmtpTransport {
                         Ok(builder.credentials(creds).build())
                     }
                 }
-                Starttls::Opportunistic | Starttls::Always => {
+                Starttls::Always => {
                     // STARTTLS - typically port 587
                     tracing::event!(target: "backend::contact", tracing::Level::DEBUG, "Using STARTTLS");
                     let creds = Credentials::new(settings.user.clone(), settings.password.clone());
@@ -429,23 +429,6 @@ mod tests {
         assert!(result.is_ok());
     }
 
-    #[test]
-    fn smtp_transport_starttls_opportunistic() {
-        let settings = EmailSettings {
-            host: "smtp.example.com".to_string(),
-            port: 587,
-            user: "user@example.com".to_string(),
-            password: "password".to_string(),
-            from: "from@example.com".to_string(),
-            recipient: "to@example.com".to_string(),
-            tls: false,
-            starttls: Starttls::Opportunistic,
-        };
-
-        let result = SmtpTransport::try_from(&settings);
-        assert!(result.is_ok());
-    }
-
     #[test]
     fn smtp_transport_no_encryption_with_credentials() {
         let settings = EmailSettings {

src/settings.rs

@@ -196,8 +196,6 @@ pub enum Starttls {
     /// Never use STARTTLS (unencrypted connection)
     #[default]
     Never,
-    /// Use STARTTLS if available (opportunistic encryption)
-    Opportunistic,
     /// Always use STARTTLS (required encryption)
     Always,
 }
@@ -208,10 +206,9 @@ impl TryFrom<&str> for Starttls {
     fn try_from(value: &str) -> Result<Self, Self::Error> {
         match value.to_lowercase().as_str() {
             "off" | "no" | "never" => Ok(Self::Never),
-            "opportunistic" => Ok(Self::Opportunistic),
             "yes" | "always" => Ok(Self::Always),
             other => Err(format!(
-                "{other} is not a supported option. Use either `yes`, `no`, or `opportunistic`"
+                "{other} is not a supported option. Use either `yes` or `no`"
             )),
         }
     }
@@ -234,7 +231,6 @@ impl std::fmt::Display for Starttls {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let self_str = match self {
             Self::Never => "never",
-            Self::Opportunistic => "opportunistic",
             Self::Always => "always",
         };
         write!(f, "{self_str}")
@@ -252,7 +248,7 @@ impl<'de> serde::Deserialize<'de> for Starttls {
             type Value = Starttls;
 
             fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
-                formatter.write_str("a string or boolean representing STARTTLS setting (e.g., 'yes', 'no', 'opportunistic', true, false)")
+                formatter.write_str("a string or boolean representing STARTTLS setting (e.g., 'yes', 'no', true, false)")
             }
 
             fn visit_str<E>(self, value: &str) -> Result<Starttls, E>
@@ -434,13 +430,6 @@ mod tests {
         assert_eq!(result, Starttls::Always);
     }
 
-    #[test]
-    fn startls_deserialize_from_string_opportunistic() {
-        let json = r#""opportunistic""#;
-        let result: Starttls = serde_json::from_str(json).unwrap();
-        assert_eq!(result, Starttls::Opportunistic);
-    }
-
     #[test]
     fn startls_deserialize_from_bool() {
         let json = "true";
@@ -482,18 +471,6 @@ mod tests {
         assert_eq!(Starttls::try_from("Yes").unwrap(), Starttls::Always);
     }
 
-    #[test]
-    fn startls_try_from_str_opportunistic() {
-        assert_eq!(
-            Starttls::try_from("opportunistic").unwrap(),
-            Starttls::Opportunistic
-        );
-        assert_eq!(
-            Starttls::try_from("OPPORTUNISTIC").unwrap(),
-            Starttls::Opportunistic
-        );
-    }
-
     #[test]
     fn startls_try_from_str_invalid() {
         let result = Starttls::try_from("invalid");
@@ -517,14 +494,6 @@ mod tests {
         );
     }
 
-    #[test]
-    fn startls_try_from_string_opportunistic() {
-        assert_eq!(
-            Starttls::try_from("opportunistic".to_string()).unwrap(),
-            Starttls::Opportunistic
-        );
-    }
-
     #[test]
     fn startls_try_from_string_invalid() {
         let result = Starttls::try_from("invalid".to_string());
@@ -553,12 +522,6 @@ mod tests {
         assert_eq!(startls.to_string(), "always");
     }
 
-    #[test]
-    fn startls_display_opportunistic() {
-        let startls = Starttls::Opportunistic;
-        assert_eq!(startls.to_string(), "opportunistic");
-    }
-
     #[test]
     fn rate_limit_settings_default() {
         let settings = RateLimitSettings::default();