diff --git a/README.md b/README.md
index 1dd33bf6..0a8f36c5 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,8 @@ Wild Duck is a distributed IMAP/POP3 server built with Node.js, MongoDB and Redi
 
 > **NB!** Wild Duck is currently in **beta**. Use it on your own responsibility.
 
+*Distributed* means that Wild Duck uses a distributed database as a backend for storing emails. Wild Duck instances are also stateless, you can have multiple instances running and a client can connect to any of these. Wild Duck uses a write ahead log to keep different IMAP sessions in sync between different instances.
+
 ## Usage
 
 Assuming you have MongoDB and Redis running somewhere.
@@ -444,7 +446,14 @@ Shard the following collections by these keys:
 
 * Collection: `messages`, key: `user` (by hash?)
 * Collection: `attachment.files`, key: `_id` (by hash)
-* Collection: `attachment.chunks`, key: `file_id` (by hash)
+* Collection: `attachment.chunks`, key: `files_id` (by hash)
+
+```javascript
+sh.enableSharding('wildduck');
+sh.shardCollection('wildduck.messages', { user: 'hashed' });
+sh.shardCollection('wildduck.attachments.files', { 'metadata.h': 'hashed' });
+sh.shardCollection('wildduck.attachments.chunks', { files_id: 'hashed' });
+```
 
 ## IMAP Protocol Differences
 
diff --git a/imap.js b/imap.js
index 3db92b6c..e1dcde01 100644
--- a/imap.js
+++ b/imap.js
@@ -23,7 +23,7 @@ const setupIndexes = yaml.safeLoad(fs.readFileSync(__dirname + '/indexes.yaml',
 const BULK_BATCH_SIZE = 150;
 
 // how often to clear expired messages
-const GC_INTERVAL = 10 * 60 * 1000;
+const GC_INTERVAL = 0.1 * 60 * 1000;
 
 // artificail delay between deleting next expired message in ms
 const GC_DELAY_DELETE = 100;
diff --git a/indexes.yaml b/indexes.yaml
index b7323dab..e75e73c6 100644
--- a/indexes.yaml
+++ b/indexes.yaml
@@ -55,6 +55,13 @@ indexes:
 # key should be 'user' so keep this field as the first one
 # in indexes
 
+- collection: messages
+  index:
+    # hashed index needed for sharding
+    name: messages_shard
+    key:
+      user: hashed
+
 - collection: messages
   index:
     name: mailbox_by_id
@@ -215,13 +222,19 @@ indexes:
   index:
     name: attachment_hash
     key:
-      metadata.h: 1
+      metadata.h: hashed
 - collection: attachments.files
   index:
     name: related_attachments
     key:
       metadata.c: 1
       metadata.m: 1
+- collection: attachments.chunks
+  index:
+    # hashed index needed for sharding
+    name: chunks_shard
+    key:
+      files_id: hashed
 
 # Indexes for the journal collection
 
diff --git a/lib/message-handler.js b/lib/message-handler.js
index 70aea1d1..21515167 100644
--- a/lib/message-handler.js
+++ b/lib/message-handler.js
@@ -762,9 +762,9 @@ class MessageHandler {
         let envelope = this.indexer.getEnvelope(mimeTree);
 
         let idate = (options.date && parseDate(options.date)) || new Date();
-        let hdate = (mimeTree.parsedHeader.date && parseDate(mimeTree.parsedHeader.date, idate)) || false;
+        let hdate = (mimeTree.parsedHeader.date && parseDate([].concat(mimeTree.parsedHeader.date || []).pop() || '', idate)) || false;
 
-        let subject = (mimeTree.parsedHeader.subject || '').trim();
+        let subject = ([].concat(mimeTree.parsedHeader.subject || []).pop() || '').trim();
         try {
             subject = libmime.decodeWords(subject);
         } catch (E) {
@@ -801,10 +801,10 @@ class MessageHandler {
     getThreadId(userId, subject, mimeTree, callback) {
         let referenceIds = new Set(
             [
-                mimeTree.parsedHeader['message-id'] || '',
-                mimeTree.parsedHeader['in-reply-to'] || '',
-                (mimeTree.parsedHeader['thread-index'] || '').substr(0, 22),
-                mimeTree.parsedHeader.references || ''
+                [].concat(mimeTree.parsedHeader['message-id'] || []).pop() || '',
+                [].concat(mimeTree.parsedHeader['in-reply-to'] || []).pop() || '',
+                ([].concat(mimeTree.parsedHeader['thread-index'] || []).pop() || '').substr(0, 22),
+                [].concat(mimeTree.parsedHeader.references || []).pop() || ''
             ]
                 .join(' ')
                 .split(/\s+/)