Outlook email stuck in Outbox

[PJamesH]

My wife and I have had NTLWORLD.COM email addresses ever since they were first available.

We both use Outlook.

My email is working O.K. but, since the end of May, my wife's can receive mail but sent mail gets stuck in Outbox. 

error (0x800CCC78) Cannot send the message. Verify the email address in your account properties. The server responded 530 5.1.0 Authentication required (VM401)

No changes have been made, so I am a loss to know why this has happened.

[Graham_A]

@PJamesH  Go into the settings section for the email account in outlook and on the Outgoing server tab make sure that My outgoing server (smtp) requires authentication is ticked and select the option - use same settings as my incoming mail server.

[PJamesH]

Sorted. Thank you. I just wish I knew how and why that feature was disabled.