I have added my work email account as a send and receive account to my outlook.com account.

I am receiving emails successfully, and was previously able to send emails from my work address via my outlook.com account.

However, when I now try to send emails via outlook.com, I receive a Mail Delivery Status Notification (Failure) email from *** Email address is removed for privacy ***. I have checked the incoming server settings and these are correct. I have phoned my work email provider (the phone co-op) who say the problem is with hotmail, and is not something they can do anything about. Any ideas much appreciated! Thanks