Workaround protocol parameter missing

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

@@ -2145,9 +2145,32 @@ public class MessageHelper {
 
         try {
             if (imessage instanceof IMAPMessage) {
-                if (body)
-                    imessage.getContentType(); // force loadBODYSTRUCTURE
-                else
+                if (body) {
+                    String contentType = imessage.getContentType(); // force loadBODYSTRUCTURE
+
+                    // Workaround protocol parameter missing
+                    // Happens with Yandex and possibly other providers
+                    boolean load = false;
+                    try {
+                        ContentType ct = new ContentType(contentType);
+                        if (ct.match("multipart/signed") || ct.match("multipart/encrypted")) {
+                            String protocol = ct.getParameter("protocol");
+                            if (protocol == null)
+                                load = true;
+                        } else if (ct.match("application/pkcs7-mime") || ct.match("application/x-pkcs7-mime")) {
+                            String smimeType = ct.getParameter("smime-type");
+                            if (smimeType == null)
+                                load = true;
+                        }
+                    } catch (Throwable ex) {
+                        Log.w(ex);
+                    }
+
+                    if (load) {
+                        Log.w("Protocol missing content-type=" + contentType);
+                        throw new MessagingException("Failed to load IMAP envelope");
+                    }
+                } else
                     imessage.getMessageID(); // force loadEnvelope
             }
         } catch (MessagingException ex) {