Security News > 2021 > January > SpamCop anti-spam service suffers an outage after its domain expired
Cisco's SpamCop anti-spam service suffered an outage Sunday after its domain was mistakenly allowed to expire.
SpamCop provides a Real-time Blackhole List that mail servers can use to determine if incoming mail should be considered spam.
Mail servers that use the SpamCop RBL service perform a DNS lookup of a connecting mail server's IP address to check if it is known to be used for spam.
If an outgoing mail server at IP address 192.168.1.2 connects to an incoming mail server using SpamCop, the incoming mail server will perform a DNS lookup for 2.1.168.192.bl.
If the SpamCop service returns a result, then the outgoing mail server is considered a spam relay, and the email is rejected.
Today, mail administrators, organizations, and ISPs worldwide suddenly found that their outgoing mail was being rejected by mail servers using the SpamCop service.