Summary: This problem is caused when one of messages in the Outbox is corrupt.
Resolution: In most cases it can be resolved by moving the messages from the Outbox to the Drafts folder, and then sending them one by one. One of the messages will fail to send; this message must be deleted and re-created from scratch.
If the message can not even be moved to another folder, the problem is that Outlook Express’ message index is corrupted. To fix this, select File > Folder > Compact all folders. This can take a while depending on the size of the message index, but after it is finished everything should work again.
Resolution: In most cases it can be resolved by moving the messages from the Outbox to the Drafts folder, and then sending them one by one. One of the messages will fail to send; this message must be deleted and re-created from scratch.
If the message can not even be moved to another folder, the problem is that Outlook Express’ message index is corrupted. To fix this, select File > Folder > Compact all folders. This can take a while depending on the size of the message index, but after it is finished everything should work again.
