Added support for Mail-Followup-To and Mail-Followup-To headers (untested)

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -1211,6 +1211,14 @@ public class MessageHelper {
     }
 
     Address[] getCc() throws MessagingException {
+        try {
+            // https://cr.yp.to/proto/replyto.html
+            Address[] a = getAddressHeader("Mail-Followup-To");
+            if (a != null)
+                return a;
+        } catch (MessagingException ex) {
+            Log.e(ex);
+        }
         return getAddressHeader("Cc");
     }
 
@@ -1219,6 +1227,14 @@ public class MessageHelper {
     }
 
     Address[] getReply() throws MessagingException {
+        try {
+            // https://cr.yp.to/proto/replyto.html
+            Address[] a = getAddressHeader("Mail-Reply-To");
+            if (a != null)
+                return a;
+        } catch (MessagingException ex) {
+            Log.e(ex);
+        }
         return getAddressHeader("Reply-To");
     }