I get this message when trying to send an email from my linux laptop: An error occurred while sending mail. The mail server responded: 451 5.7.3 STARTTLS is required to send mail [CO2PR04CA0178.namprd04.prod.outlook.com]. Please verify that your email address is correct in your account settings and try again. Background: My email server was recently migrated to office365. Many features worked okay until 24 hours later. The email support person (from godaddy) walked me through updating the incoming and outgoing server addresses, but had no idea what to make of this error message. Can anyone help walk me through whats going on and how to fix it? Thanks!