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cmack0
Posts: 1
Registered: ‎02-15-2012

RDNS failures

When sending mail to comcast accounts our mail gateways are receiving a Reverse DNS failure:

 

Starting SMTP test of host mx2.comcast.net.
Resolved 'mx2.comcast.net' to 76.96.30.116.
Connection to 76.96.30.116 succeeded.
Connection rejected. Remote server said: 421 ['imta19.emeryville.ca.mail.comcast.net comcast Reverse DNS failure : Try again later']

 

I have used nslookup to query 75.75.75.75 and reverse lookup returns the correct name but the comcast mail servers still are rejecting our connections.

 

Our IPs are 136.160.171.31 and .32 We are able to send to AOL, gmail, msn, virtually everywhere else but comcast. 

Bronze Problem Solver
Posts: 3,281
Registered: ‎05-12-2006

Re: RDNS failures


cmack0 wrote:

When sending mail to comcast accounts our mail gateways are receiving a Reverse DNS failure:

 

Starting SMTP test of host mx2.comcast.net.
Resolved 'mx2.comcast.net' to 76.96.30.116.
Connection to 76.96.30.116 succeeded.
Connection rejected. Remote server said: 421 ['imta19.emeryville.ca.mail.comcast.net comcast Reverse DNS failure : Try again later']

 

I have used nslookup to query 75.75.75.75 and reverse lookup returns the correct name but the comcast mail servers still are rejecting our connections.

 

Our IPs are 136.160.171.31 and .32 We are able to send to AOL, gmail, msn, virtually everywhere else but comcast. 


Here are the DNS servers listed for that range of addresses. Trantor.umd.edu isn't answering queries, so sometimes there won't be a DNS answer one way or the other, which will result in that "try again later" error from Comcast.

 

136.in-addr.arpa.       86400   IN      NS      v.arin.net.
136.in-addr.arpa.       86400   IN      NS      dill.arin.net.
136.in-addr.arpa.       86400   IN      NS      y.arin.net.
136.in-addr.arpa.       86400   IN      NS      u.arin.net.
136.in-addr.arpa.       86400   IN      NS      z.arin.net.
136.in-addr.arpa.       86400   IN      NS      x.arin.net.
136.in-addr.arpa.       86400   IN      NS      t.arin.net.
136.in-addr.arpa.       86400   IN      NS      w.arin.net.
;; Received 184 bytes from 199.212.0.73#53(a.in-addr-servers.arpa) in 67 ms

160.136.in-addr.arpa.   86400   IN      NS      umcpnoc.ums.edu.
160.136.in-addr.arpa.   86400   IN      NS      trantor.umd.edu.
160.136.in-addr.arpa.   86400   IN      NS      noc.usmd.edu.
160.136.in-addr.arpa.   86400   IN      NS      ns.usmd.edu.
;; Received 140 bytes from 63.243.194.2#53(v.arin.net) in 61 ms

171.160.136.in-addr.arpa. 86400 IN      NS      ns1.towson.edu.
171.160.136.in-addr.arpa. 86400 IN      NS      trantor.umd.edu.
171.160.136.in-addr.arpa. 86400 IN      NS      ns2.towson.edu.