South African Internet users may find themselves unable to send emails due to their IP addresses being blacklisted.
A Supersonic customer using MTN’s fixed-LTE product recently told MyBroadband that his connection was repeatedly being assigned to blacklisted IP addresses.
He noticed the issue after attempting to send an email, after which he would receive a return message that stated his IP was blacklisted.
He attempted to fix the issue by rebooting his router, so he would be assigned a new IP address, but found that he was still unable to send emails. This was because every consecutive IP address allocated was also blacklisted.
In many instances, IPs are blacklisted for legitimate reasons.
As detailed by MailChannels, a company that specialises in security products for email hosting providers, an IP blacklist is a database of IP addresses or domains that are known sources of spam.
These are often referred to as Domain Name System Blacklists (DNSBLs).
Most message transfer agents (MTAs) are able to reject or flag messages received from a blacklisted IP. This results in either the message being placed in a spam or junk folder, or being completely rejected.
Two main types of blacklists exist: IP-based and Domain-based.
IP-based blacklists contain the addresses of servers known to be sending spam, while domain-based URI blacklists (URI DNSBLs) hold a list of domain names.
These blacklists search for URLs in the body of the email to determine whether it contains a domain that has been marked as a source of spam.
There are hundreds of blacklist databases on which an IP or domains might appear, and notable ones include Spamhaus, Spamcop, Invaluement, and Barracuda Reputation Block List.
MTN Executive for Corporate Affairs Jacqui O’Sullivan said there are several reasons why an MTN customer’s IP may be blacklisted.
This includes if the IP has been identified as a source of email spam or was compromised by malware, botnets, or trojans.
In the case of the particular Supersonic customer, however, MTN said that his IP wasn’t a specific target of blacklisting, but that it formed part of a blacklisted IP pool.
“The customer’s IP is part of a dynamic pool of IPs assigned to the fixed-LTE service. It is not the case that this specific customer’s IP was blacklisted, but rather that the customer was assigned an IP from a pool which has been blacklisted before,” O’Sullivan stated.
She said that the issue is not related to MTN’s network, but does occur when ISPs assign certain IPs to users.
“We are investigating the specific subnet and engaging with the blacklisting organisations to remove the blacklisting,” O’Sullivan said.
O’Sullivan said that the blacklisting and de-blacklisting of IPs is primarily a reactive process. The operator encouraged customers to notify their network providers of instances in which they claim to have had their IPs blacklisted.
MTN and Supersonic customers can contact MTN via email at [email protected] if they have been assigned a blacklisted IP.