Error handling refactor and 500 page/message templates

src/configuration.rs

@@ -81,7 +81,7 @@ pub struct EmailClientSettings {
 }
 
 impl EmailClientSettings {
-    pub fn sender(&self) -> Result<SubscriberEmail, String> {
+    pub fn sender(&self) -> Result<SubscriberEmail, anyhow::Error> {
         SubscriberEmail::parse(self.sender_email.clone())
     }