554 5.7.1 Delivery not authorized

Question

I tried to send MIT email and got the following error, what does it mean?

554 5.7.1 Delivery not authorized

Answer

Our Spam filter (Symantec Brightmail) can block various messages for various reasons.

Symantec's official answer to the topic is here:
http://www.symantec.com/docs/TECH169847 - Message Rejected with SMTP Code 554. 5.7.1

MIT-specific answer

Informally, one of the most common situations we've seen at the Help Desk are in cases where Reverse DNS is not configured properly. Loosely speaking, the problem is that server contacting MIT does not have its own hostname. (The loose description, is not technically correct - the correct technical question is whether there is a PTR record for the IP address.)

Diagnosing this can be difficult, because mail errors do not always give a good report of IP addresses. For best diagnosis, forward the error bounce as an attachment, do not merely forward its text.

Alternately, ask the sender to send test email to mrhalp@gmail.com, and then go to gmail.com and use "show original" to view the Received headers.

If DNS reverse-resolving is the issue, the sender or the sender's mail administrators would need to add a PTR record for the IP address of their server that is trying to contact MIT.

Example of error message

Here is an example of this kind of mail error

How to check DNS

You can use nslookup or host or other tools to check to see if an IP address reverse-resolves.