Support for external email addresses on mailing lists (closes #152)

crates/utils/src/lib.rs

@@ -248,3 +248,39 @@ impl ServerCertVerifier for DummyVerifier {
         ]
     }
 }
+
+// Basic email sanitizer
+pub fn sanitize_email(email: &str) -> Option<String> {
+    let mut result = String::with_capacity(email.len());
+    let mut found_local = false;
+    let mut found_domain = false;
+    let mut last_ch = char::from(0);
+
+    for ch in email.chars() {
+        if !ch.is_whitespace() {
+            if ch == '@' {
+                if !result.is_empty() && !found_local {
+                    found_local = true;
+                } else {
+                    return None;
+                }
+            } else if ch == '.' {
+                if !(last_ch.is_alphanumeric() || last_ch == '-' || last_ch == '_') {
+                    return None;
+                } else if found_local {
+                    found_domain = true;
+                }
+            }
+            last_ch = ch;
+            for ch in ch.to_lowercase() {
+                result.push(ch);
+            }
+        }
+    }
+
+    if found_domain && last_ch != '.' && psl::domain(result.as_bytes()).is_some() {
+        Some(result)
+    } else {
+        None
+    }
+}