Outlook Windows 11

This is a known Outlook behavior with some IMAP accounts such as Gmail, Yahoo, AOL, and others. The message is usually sent only once, but two copies can appear in Sent Items because the mail server saves one copy and Outlook uploads another. One of the copies may also appear as unread.

To work around it in Classic Outlook for Windows:

1. Open Outlook.
2. Select 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.

If the issue is instead that sent mail is missing, check this setting:

1. Select File > Options > Mail.
2. Under Save messages, make sure Save copies of messages in Sent Items folder is checked.

Also check whether the duplicate is in Sent Items rather than Outbox. If it is in Sent Items and the recipient only gets one message, that matches the known IMAP duplicate-sent-items issue.

References:

• IMAP Sent Messages in Outlook for Windows are duplicated and unread in Sent Items folder
• Change where sent email messages are saved
• View sent email