diff --git a/src/Messages/Interactions/TSMessage.m b/src/Messages/Interactions/TSMessage.m
index 0f5834b8..4b893c7b 100644
--- a/src/Messages/Interactions/TSMessage.m
+++ b/src/Messages/Interactions/TSMessage.m
@@ -1,5 +1,6 @@
-//  Created by Frederic Jacobs on 12/11/14.
-//  Copyright (c) 2014 Open Whisper Systems. All rights reserved.
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 #import "TSMessage.h"
 #import "NSDate+millisecondTimeStamp.h"
@@ -172,7 +173,7 @@ - (NSString *)debugDescription
         NSString *attachmentId = self.attachmentIds[0];
         return [NSString stringWithFormat:@"Media Message with attachmentId:%@", attachmentId];
     } else {
-        return [NSString stringWithFormat:@"%@ with body:%@", [self class], self.body];
+        return [NSString stringWithFormat:@"%@ with body: %@", [self class], self.body];
     }
 }
 
diff --git a/src/Messages/OWSFailedMessagesJob.h b/src/Messages/OWSFailedMessagesJob.h
new file mode 100644
index 00000000..49d8c67d
--- /dev/null
+++ b/src/Messages/OWSFailedMessagesJob.h
@@ -0,0 +1,28 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+NS_ASSUME_NONNULL_BEGIN
+
+@class TSStorageManager;
+
+@interface OWSFailedMessagesJob : NSObject
+
+- (instancetype)init NS_UNAVAILABLE;
+- (instancetype)initWithStorageManager:(TSStorageManager *)storageManager NS_DESIGNATED_INITIALIZER;
+
+- (void)run;
+
+/**
+ * Database extensions required for class to work.
+ */
+- (void)asyncRegisterDatabaseExtensions;
+
+/**
+ * Only use the sync version for testing, generally we'll want to register extensions async
+ */
+- (void)blockingRegisterDatabaseExtensions;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/src/Messages/OWSFailedMessagesJob.m b/src/Messages/OWSFailedMessagesJob.m
new file mode 100644
index 00000000..d787961e
--- /dev/null
+++ b/src/Messages/OWSFailedMessagesJob.m
@@ -0,0 +1,151 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+#import "OWSFailedMessagesJob.h"
+#import "TSMessage.h"
+#import "TSOutgoingMessage.h"
+#import "TSStorageManager.h"
+#import <YapDatabase/YapDatabaseConnection.h>
+#import <YapDatabase/YapDatabaseQuery.h>
+#import <YapDatabase/YapDatabaseSecondaryIndex.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+static NSString *const OWSFailedMessagesJobMessageStateColumn = @"message_state";
+static NSString *const OWSFailedMessagesJobMessageStateIndex = @"index_outoing_messages_on_message_state";
+
+@interface OWSFailedMessagesJob ()
+
+@property (nonatomic, readonly) TSStorageManager *storageManager;
+
+@end
+
+@implementation OWSFailedMessagesJob
+
+- (instancetype)initWithStorageManager:(TSStorageManager *)storageManager
+{
+    self = [super init];
+    if (!self) {
+        return self;
+    }
+
+    _storageManager = storageManager;
+
+    return self;
+}
+
+- (NSArray<NSString *> *)fetchAttemptingOutMessageIds:(YapDatabaseConnection *)dbConnection
+{
+    NSMutableArray<NSString *> *messageIds = [NSMutableArray new];
+
+    NSString *formattedString = [NSString stringWithFormat:@"WHERE %@ == %d",
+                                          OWSFailedMessagesJobMessageStateColumn,
+                                          (int)TSOutgoingMessageStateAttemptingOut];
+    YapDatabaseQuery *query = [YapDatabaseQuery queryWithFormat:formattedString];
+    [dbConnection readWithBlock:^(YapDatabaseReadTransaction *_Nonnull transaction) {
+        [[transaction ext:OWSFailedMessagesJobMessageStateIndex]
+            enumerateKeysMatchingQuery:query
+                            usingBlock:^void(NSString *collection, NSString *key, BOOL *stop) {
+                                [messageIds addObject:key];
+                            }];
+    }];
+
+    return [messageIds copy];
+}
+
+- (void)enumerateAttemptingOutMessagesWithBlock:(void (^_Nonnull)(TSOutgoingMessage *message))block
+{
+    YapDatabaseConnection *dbConnection = [self.storageManager newDatabaseConnection];
+
+    // Since we can't directly mutate the enumerated "attempting out" expired messages, we store only their ids in hopes
+    // of saving a little memory and then enumerate the (larger) TSMessage objects one at a time.
+    for (NSString *expiredMessageId in [self fetchAttemptingOutMessageIds:dbConnection]) {
+        TSOutgoingMessage *_Nullable message = [TSOutgoingMessage fetchObjectWithUniqueID:expiredMessageId];
+        if ([message isKindOfClass:[TSOutgoingMessage class]]) {
+            block(message);
+        } else {
+            DDLogError(@"%@ unexpected object: %@", self.tag, message);
+        }
+    }
+}
+
+- (void)run
+{
+    __block uint count = 0;
+    [self enumerateAttemptingOutMessagesWithBlock:^(TSOutgoingMessage *message) {
+        // sanity check
+        OWSAssert(message.messageState == TSOutgoingMessageStateAttemptingOut);
+        if (message.messageState != TSOutgoingMessageStateAttemptingOut) {
+            DDLogError(@"%@ Refusing to mark as unsent message with state: %d", self.tag, (int)message.messageState);
+            return;
+        }
+
+        DDLogDebug(@"%@ marking message as unsent", self.tag);
+        message.messageState = TSOutgoingMessageStateUnsent;
+        [message save];
+        count++;
+    }];
+
+    DDLogDebug(@"%@ Marked %u messages as unsent", self.tag, count);
+}
+
+#pragma mark - YapDatabaseExtension
+
+- (YapDatabaseSecondaryIndex *)indexDatabaseExtension
+{
+    YapDatabaseSecondaryIndexSetup *setup = [YapDatabaseSecondaryIndexSetup new];
+    [setup addColumn:OWSFailedMessagesJobMessageStateColumn withType:YapDatabaseSecondaryIndexTypeInteger];
+
+    YapDatabaseSecondaryIndexHandler *handler =
+        [YapDatabaseSecondaryIndexHandler withObjectBlock:^(YapDatabaseReadTransaction *transaction,
+            NSMutableDictionary *dict,
+            NSString *collection,
+            NSString *key,
+            id object) {
+            if (![object isKindOfClass:[TSOutgoingMessage class]]) {
+                return;
+            }
+            TSOutgoingMessage *message = (TSOutgoingMessage *)object;
+
+            dict[OWSFailedMessagesJobMessageStateColumn] = @(message.messageState);
+        }];
+
+    return [[YapDatabaseSecondaryIndex alloc] initWithSetup:setup handler:handler];
+}
+
+// Useful for tests, don't use in app startup path because it's slow.
+- (void)blockingRegisterDatabaseExtensions
+{
+    [self.storageManager.database registerExtension:[self indexDatabaseExtension]
+                                           withName:OWSFailedMessagesJobMessageStateIndex];
+}
+
+- (void)asyncRegisterDatabaseExtensions
+{
+    [self.storageManager.database asyncRegisterExtension:[self indexDatabaseExtension]
+                                                withName:OWSFailedMessagesJobMessageStateIndex
+                                         completionBlock:^(BOOL ready) {
+                                             if (ready) {
+                                                 DDLogDebug(@"%@ completed registering extension async.", self.tag);
+                                             } else {
+                                                 DDLogError(@"%@ failed registering extension async.", self.tag);
+                                             }
+                                         }];
+}
+
+#pragma mark - Logging
+
++ (NSString *)tag
+{
+    return [NSString stringWithFormat:@"[%@]", self.class];
+}
+
+- (NSString *)tag
+{
+    return self.class.tag;
+}
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/src/Messages/OWSMessageSender.m b/src/Messages/OWSMessageSender.m
index 4b1ee0ce..70ac96b9 100644
--- a/src/Messages/OWSMessageSender.m
+++ b/src/Messages/OWSMessageSender.m
@@ -409,6 +409,8 @@ - (void)sendMessage:(TSOutgoingMessage *)message
             success:(void (^)())successHandler
             failure:(void (^)(NSError *error))failureHandler
 {
+    DDLogDebug(@"%@ sending message to service: %@", self.tag, message.debugDescription);
+
     if (remainingAttempts <= 0) {
         // We should always fail with a specific error.
         DDLogError(@"%@ Unexpected generic failure.", self.tag);
@@ -463,6 +465,9 @@ - (void)sendMessage:(TSOutgoingMessage *)message
             });
         }
         failure:^(NSURLSessionDataTask *task, NSError *error) {
+            DDLogDebug(@"%@ failure sending to service: %@", self.tag, message.debugDescription);
+            [DDLog flushLog];
+
             NSHTTPURLResponse *response = (NSHTTPURLResponse *)task.response;
             long statuscode = response.statusCode;
             NSData *responseData = error.userInfo[AFNetworkingOperationFailingURLResponseDataErrorKey];
@@ -473,6 +478,7 @@ - (void)sendMessage:(TSOutgoingMessage *)message
                 }
 
                 dispatch_async([OWSDispatch sendingQueue], ^{
+                    DDLogDebug(@"%@ Retrying: %@", self.tag, message.debugDescription);
                     [self sendMessage:message
                             recipient:recipient
                                thread:thread
@@ -554,6 +560,9 @@ - (void)handleMessageSentLocally:(TSOutgoingMessage *)message
 {
     [self saveMessage:message withState:TSOutgoingMessageStateSent];
     if (message.shouldSyncTranscript) {
+        // TODO: I suspect we shouldn't optimistically set hasSyncedTranscript.
+        //       We could set this in a success handler for [sendSyncTranscriptForMessage:].
+
         message.hasSyncedTranscript = YES;
         [self sendSyncTranscriptForMessage:message];
     }
diff --git a/src/Storage/TSStorageManager.m b/src/Storage/TSStorageManager.m
index 34903386..83303ec4 100644
--- a/src/Storage/TSStorageManager.m
+++ b/src/Storage/TSStorageManager.m
@@ -6,6 +6,7 @@
 #import "NSData+Base64.h"
 #import "OWSAnalytics.h"
 #import "OWSDisappearingMessagesFinder.h"
+#import "OWSFailedMessagesJob.h"
 #import "OWSReadReceipt.h"
 #import "SignalRecipient.h"
 #import "TSAttachmentStream.h"
@@ -200,6 +201,8 @@ - (void)setupDatabase
     [OWSReadReceipt asyncRegisterIndexOnSenderIdAndTimestampWithDatabase:self.database];
     OWSDisappearingMessagesFinder *finder = [[OWSDisappearingMessagesFinder alloc] initWithStorageManager:self];
     [finder asyncRegisterDatabaseExtensions];
+    OWSFailedMessagesJob *failedMessagesJob = [[OWSFailedMessagesJob alloc] initWithStorageManager:self];
+    [failedMessagesJob asyncRegisterDatabaseExtensions];
 }
 
 - (void)protectSignalFiles {