550 550 This system is configured to reject mail

[chicagotech]

Q: I am test our Excahnge by running telnet mail.chicagotech.net 25, I get this message:
550 550 This system is configured to reject mail from x.x.19.39 [x.x.19.39
] (Host blacklisted - Found on Realtime Black List server 'zen.spamhaus.org')
What does that mean?

A: Apparently that remote server has a setting to reject mails when a reverse dns lookup failed

[chicagotech]

I got the issue resolved with my hosting provider because the IP did not contain an PTR record. Thanks

[chicagotech]

From my experience, the host name has to have a reverse DNS back through your ISP. Your ISP has to setup your public mail server IP to your full server host name. Use DNSStuff.com or something similar to make sure it's resolving correctly externally. Once this is setup correctly you shouldn't have a problem.

IP Information - x.x.43.202IP address: x.x.43.202
Reverse DNS: [No reverse DNS entry per ns1.msa1.illinois.net.]
Reverse DNS authenticity: [Unknown]
ASN: 6325
ASN Name: ILLINOIS-CENTURY
IP range connectivity: 2
Registrar (per ASN): ARIN
Country (per IP registrar): US [United States]
Country Currency: USD [United States Dollars]
Country IP Range: x.x.0.0 to x.x.255.255
Country fraud profile: Normal
City (per outside source): Gurnee, Illinois
Country (per outside source): US [United States]
Private (internal) IP? No
IP address registrar: whois.arin.net
Known Proxy? No
Link for WHOIS: x.x.43.202

[guest]

I hope I wasn't too quick on this fix. The e-mail server worked fine for about an hour and then started with the 5.7.1 stuff again. Now convinced that there is a disconnect somewhere between the windows API calls that mail site is using and the DNS configuation on the e-mail server, I set the primary DNS on the net card to our internal DNS server (activie directory PDC), the secondary to the internal IP for our web domain DNS, the third to our public IP for the web DNS, the fourth to our ISP's primary DNS and made an entry for the customers IP in the host file for lookup. Stopped and restarted SMTPRA and it looks like it is working again. I let you know if it hicups again.

[guest]

- mail relaying is opened on the server.
- much SPAM amount was sent from the server