Mailer Error: SMTP Error: Data not Accepted.
Possible reasons:
Your server does not allow different senders and user names
Some servers require that the sender E-mail address be the same as the E-mail address used for authentication. Check your name and match it with the user name you used to log in to the SMTP server.
The file size of the mail is large
If the body is too large, some servers will reject the message. HTML e-mails are usually larger than plain text messages, but you should try to reduce the size by removing some content or disabling embedded images.
The receiver is blacklisted or blocked
Sometimes certain E-mail addresses are blocked, and the server will reject your messages in order to prevent being blacklisted. The best solution is to choose different delivery methods.
This is a temporary problem
Sometimes, the E-mail server will respond to this error if certain limits are reached or if the send is “too fast.” Please pause your AD campaign for a while and try again later.
If you send through Amazon SES, you must verify the origin, reply, and return addresses you use in your mail.