Start collecting recipients

- Collect recipients for processed email.
- Add proper email parsing

src/mail.rs

@@ -0,0 +1,22 @@
+//
+// Husk milter
+//
+// mail functions
+//
+
+use std::ffi::CString;
+use sequoia_openpgp::packet::UserID;
+
+pub fn to_userid(rcpt: &CString) -> Option<UserID> {
+    match rcpt.to_str() {
+        Ok(s) => Some(UserID::from(s)),
+        _ => None
+    }
+}
+
+pub fn to_email(rcpt: &CString) -> Option<String> {
+    if let Some(u) = to_userid(rcpt) {
+       if let Ok(Some(e)) = u.email() { Some(e.to_string()) }
+       else { None }
+    } else { None }
+}