Cannot send emails - emails get stuck in outbox with error message as per uploaded screenshot. 
Is this sending through an outlook.com server?
Hi, I’m getting the same issue when linking to my Hotmail account. Any help would be appreciated…thanks…
The error posted by k could be because the server is not accepting messages with a from address that is different to the account that is used to login to the server.
If that is what you are trying to do, please make sure that your server allows relaying.
Thanks Gary, could you advise how I can check that ?
If you go to Menu > Tools > Accounts, the email address in User Information should be the same as the login name in Authentication.
Great - all working now. Thanks for your help.