Check interval time to send or receive email from someone.Check internet speed of sending or receiving emails, if speed is slow then increase mail server timeout session.Uninstall or temporarily disable virus scanner when you sending an email via Outlook.Potential sources of sending multiple emails in Outlook In this tutorial, you will know the reasons and solutions with the prevention of sending duplicate emails in MS Outlook at once. I mean if Outlook is sending the same email twice, thrice or multiple times then “How will manage duplicate emails in Outlook’s sent or outbox mail-folder”. The Outlook is mostly preferred in high and middle-level businesses or corporations, but when its behavior changes then what.