Hi. I use Apple Mail for my 365 Outlook email account. Since changing to a new M1 MacBook Air and Big Sur if I send an email direct from Apple Mail it does not show up at all in the 365 Outlook sent box. It shows up in the Apple Mail sent box on my Mac but only until the Mac synchs to 365 Outlook. If I send an email from my iPhone it all works fine and the sent emails gets stored straight away in the 365 Outlook sent box. Any help would be appreciated please!
Have you configured your account using IMAP? Apple mail has a feature called Mailbox Behaviours that allow you to choose where you want to save your mails- to the mail server or to the local client (on my Mac); and this can be modified per folder.