feat(email): Add SMTP support to allow mails through self hosted/custom SMTP server (#6617)

Co-authored-by: hyperswitch-bot[bot] <148525504+hyperswitch-bot[bot]@users.noreply.github.com>

crates/external_services/src/email.rs

@@ -7,6 +7,12 @@ use serde::Deserialize;
 /// Implementation of aws ses client
 pub mod ses;
 
+/// Implementation of SMTP server client
+pub mod smtp;
+
+/// Implementation of Email client when email support is disabled
+pub mod no_email;
+
 /// Custom Result type alias for Email operations.
 pub type EmailResult<T> = CustomResult<T, EmailError>;
 
@@ -114,14 +120,27 @@ dyn_clone::clone_trait_object!(EmailClient<RichText = Body>);
 
 /// List of available email clients to choose from
 #[derive(Debug, Clone, Default, Deserialize)]
-pub enum AvailableEmailClients {
+#[serde(tag = "active_email_client")]
+#[serde(rename_all = "SCREAMING_SNAKE_CASE")]
+pub enum EmailClientConfigs {
     #[default]
+    /// Default Email client to use when no client is specified
+    NoEmailClient,
     /// AWS ses email client
-    SES,
+    Ses {
+        /// AWS SES client configuration
+        aws_ses: ses::SESConfig,
+    },
+    /// Other Simple SMTP server
+    Smtp {
+        /// SMTP server configuration
+        smtp: smtp::SmtpServerConfig,
+    },
 }
 
 /// Struct that contains the settings required to construct an EmailClient.
 #[derive(Debug, Clone, Default, Deserialize)]
+#[serde(default)]
 pub struct EmailSettings {
     /// The AWS region to send SES requests to.
     pub aws_region: String,
@@ -132,11 +151,9 @@ pub struct EmailSettings {
     /// Sender email
     pub sender_email: String,
 
-    /// Configs related to AWS Simple Email Service
-    pub aws_ses: Option<ses::SESConfig>,
-
-    /// The active email client to use
-    pub active_email_client: AvailableEmailClients,
+    #[serde(flatten)]
+    /// The client specific configurations
+    pub client_config: EmailClientConfigs,
 
     /// Recipient email for recon emails
     pub recon_recipient_email: pii::Email,
@@ -145,6 +162,17 @@ pub struct EmailSettings {
     pub prod_intent_recipient_email: pii::Email,
 }
 
+impl EmailSettings {
+    /// Validation for the Email client specific configurations
+    pub fn validate(&self) -> Result<(), &'static str> {
+        match &self.client_config {
+            EmailClientConfigs::Ses { ref aws_ses } => aws_ses.validate(),
+            EmailClientConfigs::Smtp { ref smtp } => smtp.validate(),
+            EmailClientConfigs::NoEmailClient => Ok(()),
+        }
+    }
+}
+
 /// Errors that could occur from EmailClient.
 #[derive(Debug, thiserror::Error)]
 pub enum EmailError {