Someone needs to go into the email server's settings (I'm not even sure if it's Exchange/Microsoft 365, or some other server and the Office 365-based Outlook install is being used as the client, or ...) and double-check that things are set up right. I'm also wondering if the ability to send emails is through this account, or some other account that's been set up and, "It's working," but through some other account.
Whomever set up the email server/account should check on it, and that may mean it's beyond what we can try to offer here in terms of help.