DC.net actively engages in blocking mail servers on the Internet that have been designated as willfully or unknowingly engaging in distributing unsolicited e-mails or messages containing viruses.
There are a range of offenses that can trigger DC.net mail servers to block other mail servers on the Internet. Most of these provisions are initiated automatically or at the request of our users. DC.net does not intentionally try to restrict other service providers from sending messages to our customers, but we will proactively take whatever measures are necessary to protect our network and our customers.
If you are operating a mail server that has been blocked by DC.net we can provide you documentation on why the block was initiated in a very timely manner. If you think that your server has been blocked in error or you would like to get information on what steps need to be taken to remove the block, please contact DC.net's network administration staff by phone or at rbl@ctiresidential.com and we will be happy to help.
Depending on the severity of the infraction that initiated the block by DC.net's mail servers, you may be able to automatically unblock the server yourself. If you receive a "bounce back" message when trying to e-mail a DC.net address, that message will have a link in it that shows documentation on the specific e-mail headers we received which triggered the block. You may be able to lift the block by scrolling to the bottom of this screen and clicking on the unblock link. If there is no such link you will need to contact DC.net's network administration staff by phone or at rbl@ctiresidential.com to see if the block can be removed.
DC.net's mail system engages in two types of blocking. The types are Null Routing and RBL List Blocking, which type is assigned is based on the type of abuse incurred. The following are some examples of the types of abuse which will trigger the different blocking methods and what the results will be.
Null Routing Blocks
This type of blocking is reserved for the worst situations of abuse incurred by DC.net. In order to be assigned this category of blocking a mail server will have had to engaged in a network damaging type of behavior against DC.net or our customers. In order to have a Null Route block removed, the offending server must be corrected so that it can not be exploited by others to be used in this manner again. If the server administrators themselves are willfully engaging in this behavior, the server will not be unblocked.
Possible Null Route Blocking Offenses
- DDOS Attack (Distributed Denial of Service)
- Dictionary Attack (Sending to possible combinations of addresses at a domain)
Null Route Blocking Results
- IP Packets will be dropped upon entry to DC.net's network.
Null Route Blocking Remedy
- Contact DC.net's network administration department by phone or send e-mail to rbl@ctiresidential.com.
RBL List Blocking
This type of blocking can result from abuse ranging from minor mail infractions to large unsolicited mail dumps to DC.net e-mail addresses. Based on information received by other providers and our own e-mail network, our mail servers will penalize mail servers that are known for sending spam messages. If the server is not sending a large volume of spam messages the block may only last a few hours and may be removable by the mail server users or administrators. The amount of time that the mail server remains blocked is directly proportional to the amount of spam sent. If your mail server is blocked in this fashion but you do not use it to send spam messages, it has likely been exploited by someone to send spam through it. This problem can occur when running a mail system that is an "open relay," which means that anyone from any network can send mail through it. In many cases the mail server will need to be locked down so that it can not be exploited in this fashion before DC.net will lift the block on it.
Possible RBL List Blocking Offenses
- Listed on a service provider collaborative list as being known to send spam.
- DC.net receives a large volume of spam from the server.
- Server is an "open relay," allowing spam to be sent through it.
RBL List Blocking Results
- Server will be able to PING DC.net's mail system but messages to DC.net addresses will bounce.
- Server users or administrators will be able to view blocking documentation online.
- Server users or administrators may be able to unblock the server online.
- Server block may be temporary and expire automatically.
RBL List Blocking Remedy
- Lock down server so that it is no longer an "open relay".
- Take appropriate corrective action on the blocked server and unblock it via the link in the bounced message.
- Contact DC.net's network administration department by phone or send e-mail to rbl@ctiresidential.com.
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