What is dul.blackhole.cantv.net?
dul.blackhole.cantv.net is a list maintained by Cantv.net, that groups IP addresses that seem to be managed either dynamically or in large sets, by its operator. Dynamically assigned IP addresses outside of Cantv.net's networks generally should not need to directly connect directly to our email platform.
A very important fraction of all the viruses and worms we receive at Cantv.net, come from IP space assigned dynamically at other ISPs. An additional reason for rejecting those connections, is that some ISPs seem to have problems identifying the user responsible for a hostile action, so the situation becomes harder to correct.
An IP address can get into dul.blackhole.cantv.net for various reasons, among which we can cite:
The IP address does not have an inverse name associated through a resource record IN PTR in the DNS zone IN-ADDR.ARPA, pointing to a valid domain name.
Although there might be a valid inverse, the referenced name suggest to us a dynamic assignment.
Since the dynamic IP space is usually assigned in large blocks, Cantv.net will include contiguous blocks of 256 IP addresses or more (/24) to the list. The inclussion of more than a single IP address block for the same organization is justification enough for Cantv.net to escalate the entries, to include more IP space.
The rest of this page will answer questions that we frequently receive. Please review the corresponding sections, for additional information.
My mail bounces with a mention to dul.blackhole.cantv.net... Is there any problem?
Yes. Cantv.net does not want its email platform to provide service directly to computers connected to the Internet and getting dynamic IP space. With this, Cantv.net seeks to reduce the amount of viruses, worms and similar threats that must be processed by our systems. Additionally, this measure helps the operator of the dynamic space, to receive less abuse complaints.
Usually, each ISP operates one or more mail servers for its own customers' use. Users of dynamic IP space must use those servers to handle their email.
By all this, we do not mean that You send spam or unwanted mail. We simply state our preference of not receiving any mail messages from listed IP addresses, until the problem that caused the listing in the first place is resolved.
If you are an end user and observe that your email is bouncing, with a message referring you to this page, it is a very good idea to let your network administrator or ISP about this problem, as usually this is the proper contact to address this situation.
Is my IP address listed in dul.blackhole.cantv.net?
This is likely if you were referred to this page. To make sure, please write the name or IP address of the server or servers that you wish to verify in all of our lists, in the space provided below.
When using the lookup tool, the answer says "Espacio dinámico suministrado por <ISP>"... What does this mean?
The protection measures adopted by Cantv.net against unwanted email, consider the needs of other ISPs. In case that an ISP provides us with its IP assignment plan, specifying static and dynamic addresses, we will proactively add all of the dynamic IP space to our list. This reduces the amount of complaints that the ISP would need to process.
You might be receiving dynamic IP space from your ISP where a mail server might be operating. Regardless of wether your ISP contract might forbid this practice, Cantv.net won't accept connections from that IP space until a technical representative from said ISP modifies the information we have on file.
In this case, our recommendation is for you to get in touch with your ISP and request smarthosting service, which means that the ISP's mail server will receive and route email sent by your server. This usually guarantees more chances of getting your email through to more destinations.
Such a large ISP won't contact Cantv.net
The size of an ISP has no relation with its level of responsibility or the quality of its customer service. Cantv.net has received communications from ISPs with more and less users. Cantv.net also has served smaller ISPs, both with sending and receiving complaints.
The argument that "a large ISP won't talk to a smaller one" is self-imposed most of the time. When this is the effective answer from a customer service center, it is worth questioning wether the "big" ISP doesn't want to involve in the matter because it does not have the necessary controls or resources in place.
Is my domain listed in dul.blackhole.cantv.net?
No. This list never includes domains, but IP addresses. It is possible that your domain is being served from a shared server, from which the hostile activity was originated. We regret this situation, but the common practice shows that the only way to effectively protect our platform and our users, is to restrict access to IP addresses.
We're sorry for the discomfort this might cause you, and suggest that you direct your complaints about this situation, to the administrator of your own service or server as he or she is the only one responsible for this situation. Additionally, it is unlikely that Cantv.net is the only network that has taken any action as this one, as many networks block sources of abuse but lack a clear policy or tell the community what did they do.
How do I get out of dul.blackhole.cantv.net?
There's only one way to get out of dul.blackhole.cantv.net: You must convince Cantv.net that the listed IP space is not dynamically assigned. To do this, the following steps should be followed:
Make sure that all IP space within your responsability and that is associated with active equipment, have a valid IN PTR resource record, pointing to a valid domain name. This valid domain name should resolve back to the original IP address.
If your IP space complies with the prior requisite, we might consider your IP space as dynamically assigned. In this case, you must let us know which parts of your network are dynamic, in order to adjust our filters accordingly. This service might be useful for the verification of this condition.
Once you're ready to supply all of this information, use this page to contact us. Do not forget to state clearly, the IP address of the listed server and the relevant fragment of the error message. In case of using email to provide us with this information, please do not encrypt it with HTML.
Requests that do not contain complete information, only serve to delay the processing of the case. If all the information is complete, usually the removal will happen within the same working day in which it is requested. This time can be influenced by the lapse ocurred between the insertion on the list and the request for removal, as evidence needs to be archived.
Can I use your list in my servers?
Cantv.net does not publish its lists or allow third parties to use them at this time.
