diff --git a/app/src/main/java/eu/faircode/email/EntityMessage.java b/app/src/main/java/eu/faircode/email/EntityMessage.java
index 4e35c1f5fa..9922ed9715 100644
--- a/app/src/main/java/eu/faircode/email/EntityMessage.java
+++ b/app/src/main/java/eu/faircode/email/EntityMessage.java
@@ -37,7 +37,7 @@ import java.util.Arrays;
 import java.util.Date;
 import java.util.List;
 import java.util.Objects;
-import java.util.Random;
+import java.util.UUID;
 
 import javax.mail.Address;
 import javax.mail.internet.InternetAddress;
@@ -157,13 +157,7 @@ public class EntityMessage implements Serializable {
     public Long last_attempt; // send
 
     static String generateMessageId() {
-        StringBuilder sb = new StringBuilder();
-        sb.append('<')
-                .append(Math.abs(new Random().nextInt())).append('.')
-                .append(System.currentTimeMillis()).append('.')
-                .append(BuildConfig.APPLICATION_ID).append("@localhost")
-                .append('>');
-        return sb.toString();
+        return "<" + UUID.randomUUID() + "@localhost" + '>';
     }
 
     boolean replySelf(String via) {
diff --git a/app/src/main/java/eu/faircode/email/MessageHelper.java b/app/src/main/java/eu/faircode/email/MessageHelper.java
index b160ea4ecd..ea2b5a6b41 100644
--- a/app/src/main/java/eu/faircode/email/MessageHelper.java
+++ b/app/src/main/java/eu/faircode/email/MessageHelper.java
@@ -121,7 +121,7 @@ public class MessageHelper {
         if (message.inreplyto != null)
             imessage.addHeader("In-Reply-To", message.inreplyto);
 
-        imessage.addHeader("X-FairEmail-ID", message.msgid);
+        imessage.addHeader("X-Correlation-ID", message.msgid);
 
         imessage.setFlag(Flags.Flag.SEEN, message.seen);
         imessage.setFlag(Flags.Flag.FLAGGED, message.flagged);
@@ -405,7 +405,7 @@ public class MessageHelper {
 
     String getMessageID() throws MessagingException {
         // Outlook outbox -> sent
-        String header = imessage.getHeader("X-FairEmail-ID", null);
+        String header = imessage.getHeader("X-Correlation-ID", null);
         if (header == null)
             header = imessage.getHeader("Message-ID", null);
         return (header == null ? null : MimeUtility.unfold(header));