Error Message SMTP 5.5.4 Transaction failed

SMTP error 554 (Transaction failed) is one of the most vague error codes, but is typically caused by something in the From or To headers that server doesn't like.
In other words, the problem is in the sender or recipient email address.
It can be caused by

1. The sender address isn't valid.
2. The server thinks this email is spam or server IP address has been blacklisted
3. A spam trap identifying your machine as a relay, or as a machine not trusted to send mail from your domain. Make sure that you have the correct reverse DNS lookup set up.