Add support for no service resource records "null mx" (#192)

Co-authored-by: Florian Schmidt <florian.schmidt.801187200@gmail.com>
RohanNagar · Nov 20, 2023 · 1209b01 · 1209b01
1 parent 970e7a8
commit 1209b01
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Showing 2 changed files with 7 additions and 1 deletion.
diff --git a/src/main/java/com/sanctionco/jmail/dns/DNSLookupUtil.java b/src/main/java/com/sanctionco/jmail/dns/DNSLookupUtil.java
@@ -13,6 +13,7 @@
 public final class DNSLookupUtil {
   private static final int DEFAULT_INITIAL_TIMEOUT = 100;
   private static final int DEFAULT_RETRIES = 2;
+  private static final String NO_SERVICE_MX_PR_RDATA = "0 .";
 
   /**
    * Private constructor to prevent instantiation.
@@ -48,7 +49,7 @@ public static boolean hasMXRecord(String domain, int initialTimeout, int numRetr
       DirContext ctx = new InitialDirContext(env);
       Attribute attr = ctx.getAttributes(domain, new String[]{"MX"}).get("MX");
 
-      return attr != null && attr.size() > 0;
+      return attr != null && attr.size() > 0 && !attr.get(0).equals(NO_SERVICE_MX_PR_RDATA);
     } catch (NamingException e) {
       return false;
     }

diff --git a/src/test/java/com/sanctionco/jmail/dns/DNSLookupUtilTest.java b/src/test/java/com/sanctionco/jmail/dns/DNSLookupUtilTest.java
@@ -20,6 +20,11 @@ void failsToFindInvalidMXRecord() {
     assertThat(DNSLookupUtil.hasMXRecord("whatis.hello")).isFalse();
   }
 
+  @Test
+  void failsToNoServiceMXRecord() {
+    assertThat(DNSLookupUtil.hasMXRecord("gmail.de")).isFalse();
+  }
+
   @Test
   void customTimeoutWorksAsExpected() {
     long startTime = System.currentTimeMillis();