diff --git a/core/src/main/java/hudson/tasks/MailAddressResolver.java b/core/src/main/java/hudson/tasks/MailAddressResolver.java
index d914dc2..a4a55ee 100644
--- a/core/src/main/java/hudson/tasks/MailAddressResolver.java
+++ b/core/src/main/java/hudson/tasks/MailAddressResolver.java
@@ -116,7 +116,7 @@ public abstract class MailAddressResolver implements ExtensionPoint {
             return u.getFullName();
 
         String ds = Mailer.descriptor().getDefaultSuffix();
-        if(ds!=null) {
+        if (ds != null && ds.trim().length() != 0) { /* do nothing if defaultSuffix is empty */
             // another common pattern is "DOMAIN\person" in Windows. Only
             // do this when this full name is not manually set. see HUDSON-5164
             Matcher m = WINDOWS_DOMAIN_REGEXP.matcher(u.getFullName());