NOTE: This document concerns Outlook Express 4.x only and NOT Outlook Express 5.x
The error occurs because one or more messages in the Outbox is associated with a mail account configuration that either doesn't exist or is incorrectly configured.
If at least one mail account is already configured correctly in Edit > Preferences, simply double-click each message in the Outbox. This will reassign the message to the correctly configured account, and you can then click Send Now to send the message immediately, or Send Later to re-queue the message.
If no mail accounts are configured at all in Edit > Preferences, configure one as usual, then double-click each message in the Outbox to reassign the message(s) to the new account. Click Send Now to send the message immediately, or Send Later to re-queue the message.
