Increased max message size

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

@@ -129,7 +129,7 @@ public class MessageHelper {
     static final String HEADER_CORRELATION_ID = "X-Correlation-ID";
 
     private static final int MAX_HEADER_LENGTH = 998;
-    private static final int MAX_MESSAGE_SIZE = 10 * 1024 * 1024; // bytes
+    private static final int MAX_MESSAGE_SIZE = 20 * 1024 * 1024; // bytes
     private static final long ATTACHMENT_PROGRESS_UPDATE = 1500L; // milliseconds
     private static final int MAX_META_EXCERPT = 1024; // characters
     private static final int FORMAT_FLOWED_LINE_LENGTH = 72;