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.
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
If using Windows 64-bit, addins are in the following HKEY_LOCAL _MACHINE key.
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
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
- 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
- Upshot Outlook integration
- Xobni - Upgrade to the newest version of Xobni.
- RingCentral Add-in
- ABBYY PDF Addin
- Authentication problems: Are you logging on to the mail server correctly?
- No default mail account. If you can reply to messages but not send new message, check the account settings and make sure one is set as default. When you use a configuration script created by your mail provider or import accounts, an account is not always set as default.