I recently built a website for a customer and set him up with a few email addresses. The host I am using is dreamhost which I have never had any troubles with. He has been having issues with the mail accounts from time to time, mostly trying to send more than the 100 emails per hour limit that dreamhost has. Last week however he sent out an email with a number of recipients which were later returned with this error
/var/log/mail.log.2.gz:Sep 2 13:39:58 friskymail-a4 postfix/smtpd:
NOQUEUE: reject: RCPT from 126.96.36.199.in-addr.arpa[188.8.131.52]: 451
4.3.5 <************>: Recipient address rejected: Server configuration
error; from=<**********> to=<**********>
these are the actual logs minus the email addresses. I had dreamhost send them to me because I received three different answers from techs over the weekend. What is now being suggested is that this IP 184.108.40.206 is a server which the mail is being routed through prior to the dreamhost mail server. quoted from dreamhost support...
"Here are the logs that I found for the timestamp you gave me, which very
clearly indicates that a different server is resulting in these errors:"
This IP does not respond to pings. I have port scanned all the services that could be used on it with none responding.
I helped my client set his email account up over the phone so while its possible he is using some mail filter proxy I highly doubt that. Since this IP is registered to US cellular and he uses a wireless card for internet I assume this was probably his computer or USCells gateway.
I have two questions.
First, I'm not all that familiar with mail logs, especially this 451 4.3.5 error message so I am looking for some advice. Can anyone shed some light on what this error could mean?
Second, this customer sent me another email over the weekend showing another of his emails was returned. It was a different error, a timeout this time but I am starting to think that perhaps dreamhost email is not as solid as I once had thought it was. Does anyone have a suggestion of another mail service I could use for customer?
This is what Ive found so far. US CELL owns that IP and provides real IPs to their wireless customers so the 166 IP was my clients IP at the time (no worries its changed since then). The error seems to be generated by postfix address verification . Basically postfix takes an email, verifies the sender or recipient in this case by sending a blank email... just checking to see if the service is available on that server before delivering.
Recipient address rejected: Server configuration
so these addresses are being rejected because of some server configuration error. I believe the recipient servers are not responding to the postfix AR probe at all or at least not before the queued mail is rejected. More about this service here http://www.postfix.org/ADDRESS_VERIFICATION_README.html.
The silly thing is that while some of these emails are to local companies who could have their own mail servers (these I would expect to cause trouble with the address verification service) there are also many emails being returned with a gmail, yahoo, aol and roadrunner recipient address...
I sent this info to the dreamhost support staff and will provide the verdict to everyone here. Perhaps it will help someone in the future.