duplicate emails

Question

How to prevent duplicate emails from being sent in Outlook 365

Answer 1

Hi Tom Houchin,

To narrow this down, could you clarify whether two separate messages are actually reaching the recipient, or whether you only see two copies in your Sent Items folder?

Please also try sending a test message from Outlook on the web with New Outlook temporarily closed. If the message is sent only once from the web, the issue is more likely connected to the New Outlook app or its account configuration. If it is still sent twice, the mailbox configuration, a rule, or another connected service may need to be checked.

It would also help to know:

• What type of account is affected, such as Microsoft 365/Exchange, IMAP, POP, or a shared mailbox?
• Does this happen with every message or only certain messages?
• Is the same account configured in another mail app or on another device?

Please do not change the Sent Items setting yet unless the account is confirmed to be IMAP and the duplicates only appear in that folder. Thank you so much for your understanding.   

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Answer 2

If duplicate emails are being sent from an IMAP account in Outlook, the common cause is that the mail server saves a copy in Sent Items and Outlook saves another copy too.

To prevent that in Outlook for Windows:

1. Open Outlook.
2. Go to File > Account Settings > Account Settings.
3. Select the IMAP account.
4. Select Change.
5. Turn on Don't save copies of sent items.
6. Select Next, then Done.

This stops Outlook from saving its own copy, which can prevent the duplicate sent message behavior.

If the duplicate issue is specifically with meeting invites sent by a booking delegate who adds a room, that was a known Outlook service issue and the temporary guidance was to respond to the first invite and delete the duplicates.

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References:

• IMAP Sent Messages in Outlook for Windows are duplicated and unread in Sent Items folder
• Outlook users who are booking delegates that add a Room to a meeting invite may notice duplicate emails requesting responses