Is there a way to get a better explaination of SMTP error?

We are getting the following warning errors for email sent to a customer:

Final-Recipient: RFC822; [email protected]
Action: delayed
Status: 4.4.2
Diagnostic-Code: SMTP; 451 4.4.1 reply: read error from
ci.wa.us.



I am trying to figure out what this actually means, and who exactly is having the problem.
I tried testing the targeted email using network-tools.com and it worked fine. So, I am somwhat stumped on how to proceed from here.

 

Any errors in your mail log?

 

Jan 3 11:03:35 net sendmail[21954]: m03J31ep021951: to=<[email protected]>, delay=00:00:34, xdelay=00:00:31, mailer=esmtp, pri=211171, relay=mail.ci.wa.us. [1.1.1.1], dsn=4.4.2, stat=Deferred: Connection timed out with mail.ci.wa.us.


[1.1.1.1] was actually the real ip address.

 

Please check if your server got blacklisted: http://www.mxtoolbox.com/blacklists.aspx

 

nope, not BlackListed

 

Then you should ask the admin of mail.ci.wa.us why your server is blocked.

 

Another one that I don't understand

what actually is the error that happened -
4.4.7, 4.4.1 or 4.5.1 ? and why just this receipient?