Under Outgoing server, click More Options. In the left pane of the Accounts box, select the account. If you verify that your account settings are correct, but you still can't send messages, try turning on SMTP authentication.
Some email services require authentication for their SMTP server. Solution: Turn on SMTP authentication for the POP or IMAP account. Cause: Some POP and IMAP email accounts use an outgoing mail (SMTP) server that requires authentication. Solution: Verify that Outlook is online. On the Outlook menu, make sure that Work Offline is not checked. For information about checking the status of your network connections, see Mac OS Help. On a local network, see if you can access intranet sites. Use a web browser to see if you can access web sites. Solution: Make sure that your computer is connected to the Internet or your network. Cause: Outlook doesn't have a connection to the Internet or your network. Message service can be interrupted for several reasons. Outlook for Microsoft 365 for Mac Outlook 2021 for Mac Outlook 2019 for Mac Outlook 2016 for Mac Office 2016 for Mac Office for business Office 365 Small Business More.
