Move the actual logic of email parsing to EmailAddress::new() (#3656)

Very small PR; Motivation: Easier navigation using Go-To-definition.

Because, using go-to-definition of rust-analyzer on parse() doesn't take you to the actual parse() implementation but its trait definiton. On the other hand, it's very easy to find EmailAddress::new().

src/test_utils.rs

@@ -740,7 +740,7 @@ impl SentMessage {
             .split(' ')
             .next()
             .expect("no recipient found");
-        rcpt.parse().expect("failed to parse email address")
+        EmailAddress::new(rcpt).expect("failed to parse email address")
     }
 
     /// The raw message payload.