prefer X-Microsoft-Original-Message-ID, if set

outlooks SMTP-server change the Message-ID of messages
and put the original Message-ID to X-Microsoft-Original-Message-ID.

the changed Message-ID has some issues:

- outgoing messages with bcc_self enabled are shown twice
  as the self-copy got the changed Message-ID while the database uses
  the original one

- read receipts do not work as they refer to the changed message id

- in general, sender and recipient see different Message-IDs

the issues can be fixed by

(1) let all receivers use the original Message-ID

	this is what this pr is doing
    and this should fix all issues with delta-to-delta communication,
	including groups, group-images etc.
    there may be issues left in communication
	with other MUAs as they are using another Message-ID.

(2) ftr: updating the Message-ID in the database of the sender to the new one

	this requires bcc_self always enabled (which is not the case)
    and may also result easily in race conditions
    (Bob answers before Alice sees its self-sent message),
    however, has the advantage of better compatibility with other MUA.

if needed, the compatibility with other MUA could be improved by remembering
both Messages-IDs, maybe we could treat the modified as References or so,
however, i think, this could be part of another PR if we know better about
real, in the wild issues.

src/mimeparser.rs

@@ -950,7 +950,8 @@ impl MimeMessage {
     }
 
     pub fn get_rfc724_mid(&self) -> Option<String> {
-        self.get(HeaderDef::MessageId)
+        self.get(HeaderDef::XMicrosoftOriginalMessageId)
+            .or_else(|| self.get(HeaderDef::MessageId))
             .and_then(|msgid| parse_message_id(msgid).ok())
     }
 
@@ -2749,4 +2750,27 @@ On 2020-10-25, Bob wrote:
             "mime-modified test – mime-modified *set*; simplify is always regarded as lossy."
         );
     }
+
+    #[async_std::test]
+    async fn test_x_microsoft_original_message_id() {
+        let t = TestContext::new().await;
+        let message = MimeMessage::from_bytes(&t, b"Date: Wed, 17 Feb 2021 15:45:15 +0000\n\
+                Chat-Version: 1.0\n\
+                Message-ID: <DBAPR03MB1180CE51A1BFE265BD018D4790869@DBAPR03MB6691.eurprd03.prod.outlook.com>\n\
+                To: Bob <bob@example.org>\n\
+                From: Alice <alice@example.org>\n\
+                Subject: Message from Alice\n\
+                Content-Type: text/plain\n\
+                X-Microsoft-Original-Message-ID: <Mr.6Dx7ITn4w38.n9j7epIcuQI@outlook.com>\n\
+                MIME-Version: 1.0\n\
+                \n\
+                Does it work with outlook now?\n\
+                ")
+            .await
+            .unwrap();
+        assert_eq!(
+            message.get_rfc724_mid(),
+            Some("Mr.6Dx7ITn4w38.n9j7epIcuQI@outlook.com".to_string())
+        );
+    }
 }