I have an account that forwards messages automatically to my work account. Starting today, my outlook’s been pinging when these forwarded messages appear. When I go to look, though, the message has disappeared.
What the heck?
If you have rules or spam software set up to automatically delete certain messages (from certain people, with certain words inside, etc.), they will go to your Inbox, make the “sound,” and then be deleted or go wherever the rule says to put them.
Check your Inbox, all subfolders to Inbox, your Junk Mail folder, and even your Deleted folder. As missbunny suggests, check what rules you have set up, if any. See if Outlook junk mail filtering is turned on.