I have been using Outlook for Mac 2011 (version 14.4.5) OK for years.

I have changed no setting in my email accounts.

Suddenly, yesterday afternoon, I started to get the error message:

"Authentication failed because Outlook doesn't support any of the available authentication methods." Error code: 17897

... when attempting to send emails.

I can receive emails OK, but I can't send.

I have checked my settings with my Service Provider and they have confirmed that they are correct. I've just set up another email client (Apple Mail) using the same settings and that works OK.

My service provider says they can't help any further because it's a software problem with Outlook.

I have been through all the steps on the Microsoft Help Page here: 

https://support.microsoft.com/en-us/kb/2492901

... and none of them resolved the issue.

Can you help?

Thanks, Glynis