Decode first received SPF header

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

@@ -2469,6 +2469,8 @@ class Core {
                             message.bimi_selector = helper.getBimiSelector();
                             message.dkim = MessageHelper.getAuthentication("dkim", authentication);
                             message.spf = MessageHelper.getAuthentication("spf", authentication);
+                            if (message.spf == null && helper.getSPF())
+                                message.spf = true;
                             message.dmarc = MessageHelper.getAuthentication("dmarc", authentication);
                             message.return_path = helper.getReturnPath();
                             message.submitter = helper.getSender();
@@ -3347,6 +3349,8 @@ class Core {
             message.bimi_selector = helper.getBimiSelector();
             message.dkim = MessageHelper.getAuthentication("dkim", authentication);
             message.spf = MessageHelper.getAuthentication("spf", authentication);
+            if (message.spf == null && helper.getSPF())
+                message.spf = true;
             message.dmarc = MessageHelper.getAuthentication("dmarc", authentication);
             message.return_path = helper.getReturnPath();
             message.submitter = helper.getSender();

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

@@ -1293,6 +1293,18 @@ public class MessageHelper {
         return result;
     }
 
+    boolean getSPF() throws MessagingException {
+        ensureHeaders();
+
+        // http://www.open-spf.org/RFC_4408/#header-field
+        String[] headers = imessage.getHeader("Received-SPF");
+        if (headers == null || headers.length < 1)
+            return false;
+
+        String spf = MimeUtility.unfold(headers[0]);
+        return (spf.trim().toLowerCase(Locale.ROOT).startsWith("pass"));
+    }
+
     private String fixEncoding(String name, String header) {
         if (header.trim().startsWith("=?"))
             return header;