Hi @11lesley ,
Welcome to the community!
You need to enable outgoing server authentication and use the same settings as the incoming server.
- In Outlook, this can be found by pressing the "More Settings" button in the account's settings, and then going to the "Outgoing Server" tab.
- In Outlook Express, go to the "Servers" tab in the account properties screen and check the box at the bottom labeled "My server requires authentication".
Can also be caused when trying to send an email to addresses on domains which don't exist. Check the email addresses for spelling.
Let us know how it will go.
Cheers!
