diff --git a/greenmail-core/src/main/java/com/icegreen/greenmail/imap/ImapSessionFolder.java b/greenmail-core/src/main/java/com/icegreen/greenmail/imap/ImapSessionFolder.java
index b3a5fc64c3..6d5d6d848f 100644
--- a/greenmail-core/src/main/java/com/icegreen/greenmail/imap/ImapSessionFolder.java
+++ b/greenmail-core/src/main/java/com/icegreen/greenmail/imap/ImapSessionFolder.java
@@ -81,10 +81,10 @@ public boolean isReadonly() {
 
     public int[] getExpunged() {
         synchronized (expungedMsns) {
-            int[] expungedMsns = new int[this.expungedMsns.size()];
-            for (int i = 0; i < expungedMsns.length; i++) {
+            int[] expungedMsnsArray = new int[this.expungedMsns.size()];
+            for (int i = 0; i < expungedMsnsArray.length; i++) {
                 int msn = this.expungedMsns.get(i);
-                expungedMsns[i] = msn;
+                expungedMsnsArray[i] = msn;
             }
             this.expungedMsns.clear();
 
@@ -92,7 +92,7 @@ public int[] getExpunged() {
             if (!(modifiedFlags.isEmpty() && !sizeChanged)) {
                 throw new IllegalStateException("Need to do this properly...");
             }
-            return expungedMsns;
+            return expungedMsnsArray;
         }
     }
 
diff --git a/greenmail-core/src/main/java/com/icegreen/greenmail/store/InMemoryStore.java b/greenmail-core/src/main/java/com/icegreen/greenmail/store/InMemoryStore.java
index d9be27590f..886f514b96 100644
--- a/greenmail-core/src/main/java/com/icegreen/greenmail/store/InMemoryStore.java
+++ b/greenmail-core/src/main/java/com/icegreen/greenmail/store/InMemoryStore.java
@@ -79,7 +79,7 @@ public void deleteMailbox(MailFolder folder) throws FolderException {
     }
 
     @Override
-    public void renameMailbox(MailFolder existingFolder, String newName) throws FolderException {
+    public void renameMailbox(MailFolder existingFolder, String newName) {
         HierarchicalFolder toRename = (HierarchicalFolder) existingFolder;
         HierarchicalFolder parent = toRename.getParent();
 
@@ -112,16 +112,16 @@ public void renameMailbox(MailFolder existingFolder, String newName) throws Fold
     }
 
     private HierarchicalFolder getInboxOrUserRootFolder(HierarchicalFolder folder) {
-        final HierarchicalFolder inboxFolder = findParentByName(folder, ImapConstants.INBOX_NAME);
+        final HierarchicalFolder inboxFolder = findParentByName(folder);
         if(null==inboxFolder) {
             return folder.getParent();
         }
         return inboxFolder.getParent();
     }
 
-    private HierarchicalFolder findParentByName(HierarchicalFolder folder, String name) {
+    private HierarchicalFolder findParentByName(HierarchicalFolder folder) {
         HierarchicalFolder currentFolder = folder;
-        while (null != currentFolder && !name.equals(currentFolder.getName())) {
+        while (null != currentFolder && !ImapConstants.INBOX_NAME.equals(currentFolder.getName())) {
             currentFolder = currentFolder.getParent();
         }
         return currentFolder;
diff --git a/greenmail-core/src/main/java/com/icegreen/greenmail/user/UserManager.java b/greenmail-core/src/main/java/com/icegreen/greenmail/user/UserManager.java
index b1667749a7..2c30c3412f 100644
--- a/greenmail-core/src/main/java/com/icegreen/greenmail/user/UserManager.java
+++ b/greenmail-core/src/main/java/com/icegreen/greenmail/user/UserManager.java
@@ -11,14 +11,15 @@
 import org.slf4j.LoggerFactory;
 
 import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
 
 public class UserManager {
     private static final Logger log = LoggerFactory.getLogger(UserManager.class);
     /**
-     * User list by their trimmed, lowercased user names
+     * User list by their trimmed, lower-cased user names
      */
-    private Map<String, GreenMailUser> loginToUser = Collections.synchronizedMap(new HashMap<String, GreenMailUser>());
-    private Map<String, GreenMailUser> emailToUser = Collections.synchronizedMap(new HashMap<String, GreenMailUser>());
+    private Map<String, GreenMailUser> loginToUser = new ConcurrentHashMap<>();
+    private Map<String, GreenMailUser> emailToUser = new ConcurrentHashMap<>();
     private ImapHostManager imapHostManager;
     private boolean authRequired = true;
 
diff --git a/greenmail-core/src/main/java/com/icegreen/greenmail/util/GreenMailUtil.java b/greenmail-core/src/main/java/com/icegreen/greenmail/util/GreenMailUtil.java
index 7cc56efcf3..8499aabf06 100644
--- a/greenmail-core/src/main/java/com/icegreen/greenmail/util/GreenMailUtil.java
+++ b/greenmail-core/src/main/java/com/icegreen/greenmail/util/GreenMailUtil.java
@@ -51,7 +51,7 @@ public static GreenMailUtil instance() {
     /**
      * Writes the content of an input stream to an output stream
      *
-     * @throws IOException
+     * @throws IOException on io error.
      */
     public static void copyStream(final InputStream src, OutputStream dest) throws IOException {
         byte[] buffer = new byte[1024];
@@ -129,7 +129,7 @@ public static int getLineCount(String str) {
     public static String getBody(Part msg) {
         String all = getWholeMessage(msg);
         int i = all.indexOf("\r\n\r\n");
-        return i < 0 ? "" /* empty body */ : all.substring(i + 4, all.length());
+        return i < 0 ? "" /* empty body */ : all.substring(i + 4);
     }
 
     /**
@@ -333,7 +333,7 @@ public static MimeMultipart createMultipartWithAttachment(String msg, final byte
 
             DataSource ds = new DataSource() {
                 @Override
-                public InputStream getInputStream() throws IOException {
+                public InputStream getInputStream() {
                     return new ByteArrayInputStream(attachment);
                 }
 
@@ -363,6 +363,12 @@ public String getName() {
         }
     }
 
+    /**
+     * Gets a JavaMail Session for given server type such as IMAP and additional props for JavaMail.
+     *
+     * @param setup     the setup type, such as <code>ServerSetup.IMAP</code>
+     * @return the JavaMail session.
+     */
     public static Session getSession(final ServerSetup setup) {
         return getSession(setup, null);
     }
@@ -375,10 +381,20 @@ public static Session getSession(final ServerSetup setup) {
      * @return the JavaMail session.
      */
     public static Session getSession(final ServerSetup setup, Properties mailProps) {
-        Properties props = setup.configureJavaMailSessionProperties(mailProps, false);
+        return getSession(setup, mailProps, false);
+    }
 
+    /**
+     * Gets a JavaMail Session for given server type such as IMAP and additional props for JavaMail.
+     *
+     * @param setup     the setup type, such as <code>ServerSetup.IMAP</code>
+     * @param mailProps additional mail properties.
+     * @param debug sets JavaMail debug properties.
+     * @return the JavaMail session.
+     */
+    public static Session getSession(final ServerSetup setup, Properties mailProps, boolean debug) {
+        Properties props = setup.configureJavaMailSessionProperties(mailProps, debug);
         log.debug("Mail session properties are {}", props);
-
         return Session.getInstance(props, null);
     }