Reverse DNS


We will reject the connection attempt of any IP address that does not have a resolvable reverse DNS, or PTR, record. Since there are two possible scenarios for a failed reverse DNS lookup for an IP, we have two different error codes that we'll return.

  • 554 5.7.1 - Connection refused. IP name lookup failed for IP.ADD.RE.SS - This error message means that we were successful in reaching an authoritative DNS server for the connecting IP's PTR record and we received a response from that server of NXDOMAIN.
  • 421 4.7.1 - Connection refused. Cannot resolve PTR record for IP.ADD.RE.SS - This error message means that attempts to resolve the PTR record for the IP yielded a DNS response of SERVFAIL, meaning either that the authoritative DNS server for the connecting IP's PTR record is not properly configured to answer for the PTR record, or our servers could not reach the authoritative servers.

If you're seeing either of these error messages, check first with the party responsible for DNS for the IP address mentioned in the rejection.


RDNS Naming Schemes

Our hodgepodge of rDNS naming schemes has caused confusion over the years for those of you who manage servers at other sites. This document will contain a list of Road Runner naming patterns you may see in your mail (or other) server logs as the PTR records of IP addresses in Road Runner space. You may see patterns in your logs that aren't mentioned here, or you may have a need for further information or clarification; if so, please contact us for clarification.

*.res.rr.com - This naming pattern indicates an IP address in Road Runner's residential customer space. This is a dynamically assigned IP address, but the always-on nature of our cable modem service means that our customers can enjoy a persistence to their IP address assignment that can last for months or longer. Our AUP does not prohibit servers in this space, but we do make available to our customers in this space SMTP servers that they may use to relay all of their outbound mail, should they so choose.

*.dialroam.rr.com - This naming pattern indicates an IP address in the pool used to support Road Runner's Dial Access service. Customers who are away from their cable modems have the ability to connect to our network using a dialup connection, allowing them to check and send email and whatnot, using the same servers that they would use from their home connection. These IP addresses are all dynamic.

*.mgw.rr.com - This naming pattern indicates an IP address used by an inbound residential email gateway (i.e., those hosts advertised as MX records for our various residential email domains) and the DNS servers that support them.

*.va.rr.com, *.eng.rr.com, *.qa.rr.com, *.bsseng.rr.com, *.security.rr.com, *.sec.rr.com - These naming patterns indicate IP addresses used in various capacities by Time Warner Cable/Road Runner employees at Road Runner Headquarters in Herndon, VA.

*.nyroc.rr.com, *.rdc-nyc.rr.com, *.southeast.rr.com, *.tampabay.rr.com, *.texas.rr.com, *.rdc-kc.rr.com, *.columbus.rr.com, *.orange.rr.com - These naming patterns indicate IP addresses assigned to our various data centers; servers, network gear, etc.

ms-smtp-*.*.rr.com, *.mail.rr.com, mta[1-8].adephia.net, web*.mail.adelphia.net - These naming patterns are what's used for our residential outbound email gateways. These hosts are also in many of the networks mentioned in the rr.com and roadrunner.com SPF records (Time Warner Cable/Road Runner acquired many of the assets of Adelphia in 2006):

# dig a._spf.rr.com txt "v=spf1 ip4:75.180.132.0/24 ip4:71.74.56.0/24 ip4:107.14.166.0/24 ip4:107.14.73.0/24 ~all"

# dig b._spf.rr.com txt "v=spf1 ip4:24.28.200.0/24 ip4:24.93.47.0/24 ip4:24.29.109.0/24 ip4:24.24.2.0/24 +mx ~all"

# dig c._spf.rr.com txt "v=spf1 redirect=adelphia.net"

# dig adelphia.net txt "v=spf1 ip4:68.168.78.0/24 ip4:68.168.75.0/24 ip4:75.180.132.0/24 ip4:71.74.56.0/24 ~all"

For IP address A.B.C.D, this naming pattern:

rrcs-A-B-C-D.(central|ma|midsouth|nyc|nys|se|sw|west).biz.rr.com

indicates the default rDNS entry for a Road Runner Business Class customer. This IP address may be either static or dynamic; we do offer non-default rDNS to our static Business Class customers, but not all take advantage of this offer.

indicates servers and network gear deployed and managed by Road Runner personnel to support Road Runner's Business Class product offerings, including email.

(mx?|email-out-*).biz.rr.com - Road Runner managed servers deployed in support of the Road Runner Business Class email product offering.

rrcs-(asg|mta|mx|fep)-*.*.rr.com - Road Runner managed servers deployed in support of the Road Runner Business Class email product offering.

mta-*.voip.*.rr.com and mta-*.ddns.*.rr.com - This naming pattern indicates IP addresses which are used in support of Road Runner's VoIP product, Digital Phone. "MTA" in these names does not mean "Mail Transport Agent"; instead, it means "Multimedia Terminal Adapter".