After viewing the Outbox, messages won't send

If you view the Outbox while messages are waiting to be sent, the messages are marked as read and won't send.

This is caused by a Net framework add-in you have installed that 'reads' Outlook items, including the Send to OneNote addin, BCM (Business Contact Manager), and more recently, the iCloud add-in installed by iTunes. A list of other add-ins known to cause this behavior is listed below.

After Installing iCloud, Mail Won't Send? | Messages are stuck in the Outbox

Antivirus/security software is often the culprit as it is looking for viruses and spam. Disable add-ins installed by the security software to solve.

iCloud is quickly passing Anti-virus add-ins as a frequent cause. It's installed by iTunes and if you are not using syncing with an Apple device using iCloud, you can disable it. Apple also installs two additional add-ins (Change Notifier and Outlook Add-in) that are not needed if you don't sync with an Apple device. If you are using iCloud, avoid viewing the Outbox and switch to another folder before re-sending messages you opened from the Outbox. See Outlook and iCloud 2: What you need to know for the more information.

To send the affected messages, you'll need to open the message, then switch to a different folder before clicking Send on the message. Do not go open the Outbox until after the messages are sent.

To identify the add-in that results in this behavior:

If using Outlook 2003: Look in Tools, Options, Other, Advanced, Com add-ins. Disable the add-ins and re-enable them one at a time and test.
Outlook 2007: Look in Tools, Trust Center, Add-ins.
Outlook 2010: File tab, Options, Add-ins.
Outlook 2013: File tab, Options, Add-ins.

Click Go button at the bottom of the dialog to disable add-ins. Select Disabled Add-ins from the dropdown menu to re-enable add-ins.

Since BCM and possibly other add-ins are not listed in the COM add-in list, check
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins

HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins

If using Windows 64-bit, addins are in the following HKEY_LOCAL _MACHINE key.

HKEY_LOCAL_MACHINE\Software\WOW6432Node\Microsoft\Office\Outlook\AddIns

When you use a 64-bit OS, some add-ins are listed under both HKEY_LOCAL_MACHINE locations. Check the HKEY_LOCAL _MACHINE\Software\WOW6432Node path first but if its listed in both locations, you may need to set LoadBehavior to 0 in both locations.

Export the keys then change the LoadBehavior value to 0 to disconnect an add-in. Restart Outlook and test.

If you need a quick tutorial on editing the registry, see How to Edit the Registry

Applications responsible

The following is a list of some of the applications which are reported to cause message to be marked as read. If you use these or any other add-ins, check for a newer version or an update - newer versions of some of these applications will not cause problems. If the problem is caused by the newest version, disable or uninstall the addin.

• iCloud addin. used to sync with Apple devices. Disable if you are not using it to sync.
• AVG (Free version tested) - disable avgoutlook.Addin. Set LoadBehavior 0. (From "Thunderbird": you need to disable two keys for avgoutlook.Addin when using 64-bit Windows 7)
• Bitdefender Internet Security
• Symantec Endpoint Protection
• Social Connector with Outlook 2007

If you are using one of these older applications, look for a newer version:

• Evernote Clipper
• Business Contact Manager (BCM)
• Send to OneNote from Outlook PowerToy
• Outlock
• Outlook Backup Add-in
• Sierra Wireless Outlook Integration - disable in the registry. It's listed at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins\ SwiOutlookInt.Addin
• Timeslips add-in
• Attensa for Outlook. Check for upgrade: newer versions not affected.
• Cisco Meetingplace plug-in
• MindJet Mind Manager 6. Disable the add-in in the registry - the key is Mindjet.Mm6OutlookLinker.AddIn.2
• ScanSoft PDF Converter Outlook Addin
• Norton AntiSpam Outlook Plugin
• Norton Internet Security
• Salesforce
• Upshot Outlook integration
• Xobni - Upgrade to the newest version of Xobni.
• Auto-Mate
• RingCentral Add-in
• DesktopSMS.Addin
• ABBYY PDF Addin