Why Does Outlook Resend Emails?

This often happens when you are using a virus scanner that integrates with Outlook or when your Send/Receive interval is set to a very short time. In some cases, especially when you have a slow connection to your mail host, extending the mail server time-out may solve it as well.

How do I stop Outlook from resending emails?

Uncheck the "Send mail items" box in the Account Options section and then click "OK" to stop Outlook from sending emails.

Why are emails duplicating in Outlook?

The reason there are duplicates in the Sent Items folder for some email providers is that the server automatically creates an item in the Sent Items and Outlook uploads the same item again. For Read/Unread status of an email Outlook relies on the server. If the status from server is unread Outlook sets it accordingly.