Important email completely disappeared when sending

Hi,

Unfortunately, the error message suggests the message was never successfully submitted to Exchange Online because Outlook failed while uploading the attachment:

Failed to upload attachments to server (0x80040305)

When this happens, Outlook may create the message locally, attempt to upload it, then remove the local copy after the send operation fails. In some cases, the message never reaches Drafts, Sent Items, or the server at all.

Before assuming it is lost, I would check the following:

1. Recover Deleted Items
   • Outlook → Deleted Items → Recover items deleted from this folder.
2. Search all Outlook folders
   • Search for a unique word or phrase from the email body.
   • Also search for the attachment name.
3. Check Outlook Web App (OWA)
   • Sign in via Outlook on the web
   • Check Drafts, Sent Items, Deleted Items, and Recover Deleted Items.
4. Check the local Outlook cache
   • If you were using the New Outlook desktop app, the message may have been cached locally before the failure occurred.
   • Look in:
     • Drafts
     • Sync Issues folders (if using classic Outlook)
     • Recovered Items
5. If the attached email was recently received
   • Open that attached email and check whether any of the text you wrote was accidentally saved as notes, comments, or a draft reply.

If the message cannot be found in Outlook Desktop, Outlook Web, Deleted Items, Recover Deleted Items, or a search of all folders, then the message content was likely never committed to the mailbox and may not be recoverable.

Going forward, if you're using New Outlook, consider enabling automatic draft saving and, for lengthy emails, drafting them in Outlook on the web or a document first. There have been reports of draft and attachment-related issues in some New Outlook builds.