feat: hide the To header in encrypted messages

Author: link2xt

src/chat/chat_tests.rs

@@ -774,15 +774,6 @@ async fn test_self_talk() -> Result<()> {
     assert!(msg.get_showpadlock());
 
     let sent_msg = t.pop_sent_msg().await;
-    let payload = sent_msg.payload();
-    // Make sure the `To` field contains the address and not
-    // "undisclosed recipients".
-    // Otherwise Delta Chat core <1.153.0 assigns the message
-    // to the trash chat.
-    assert_eq!(
-        payload.match_indices("To: <[email protected]>\r\n").count(),
-        1
-    );
 
     let t2 = TestContext::new_alice().await;
     t2.recv_msg(&sent_msg).await;

src/mimefactory.rs

@@ -8,7 +8,7 @@ use anyhow::{bail, Context as _, Result};
 use base64::Engine as _;
 use chrono::TimeZone;
 use deltachat_contact_tools::sanitize_bidi_characters;
-use mail_builder::headers::address::{Address, EmailAddress};
+use mail_builder::headers::address::Address;
 use mail_builder::headers::HeaderType;
 use mail_builder::mime::MimePart;
 use tokio::fs;
@@ -890,18 +890,10 @@ impl MimeFactory {
                 if is_encrypted {
                     unprotected_headers.push((
                         original_header_name,
-                        Address::new_list(
-                            to.clone()
-                                .into_iter()
-                                .filter_map(|header| match header {
-                                    Address::Address(mb) => Some(Address::Address(EmailAddress {
-                                        name: None,
-                                        email: mb.email,
-                                    })),
-                                    _ => None,
-                                })
-                                .collect::<Vec<_>>(),
-                        )
+                        Address::new_list(vec![Address::new_group(
+                            Some("hidden-recipients".to_string()),
+                            Vec::new(),
+                        )])
                         .into(),
                     ));
                 } else {