Though Outlook is a professional email client with advanced features, it sometimes happens that a user has sent a mail, but the other user has not received it and of course, you will not see the item in the Sent Items folder as well. Most of the Office 365 users manage their emails using MS Outlook application. Sometimes, when there is a problem in the email server, then the sent emails are not in the Sent Items folder, but they are stuck in the Outbox folder. The new emails are in the inbox, and the sent emails are in the Sent Items folder. The Microsoft 365 account is managed in the Outlook application to send/receive emails.
