Error: Relay Access Denied

I added a new domain to my Office 365 account. I cannot send emails to accounts using this domain name. All mail is rejected with 550 5.4.1 Relay Access Denied.

I tried the solution on http://www.cgoosen.com/2011/07/moving-from-bpos-to-office365-550-5-4-1-relay-access-denied/  since in the past I possibly used it to try out the BPOS offering. This didn't help.