If you are using i Cloud and messages get stuck, see Outlook and i Cloud 2: What you need to know for the latest information.
The log files will have the extension and may be in an Outlook Logging subfolder.
How to enable transport logging in Outlook (MSKB) When you have a hidden message that won't send, it's a stuck read receipt.
They are stored as hidden messages at the root level of your mailbox.
There are two methods that can be used to delete them: 1.
In Windows 7, 8 and Vista the SRS file is at Reboot and disable the problem program before starting Outlook.