Understanding Suspicious IP Address and Mail Spoofing Attempts
We have recently experienced suspicious email spoofing attacks and noticed that our outgoing emails were marked as spam. Upon checking our mail reputation on talosintelligence.com, we found an interesting observation that we need to understand better.
There is another IP address listed for our mail domain ‘mail-gw33.credit-suisse.com’, which does not belong to us. This raises several questions:
- What does the Hostname on talosintelligence.com mean?
- If the suspicious IP address was reverse resolved to our domain, how is this possible?
- What does the number ‘LAST MONTH VOL.’ on talosintelligence.com indicate?
- Can our reputation suffer from hijacking our domain?
- How can we mitigate this in the future?
The meaning of the Hostname on talosintelligence.com refers to the HELO (or EHLO) string used to identify the sending mail server during the SMTP handshake. It is not a reliable indicator and can be easily manipulated.
To address mail spoofing attempts, it is recommended to implement Sender Policy Framework (SPF) and Domain-based Message Authentication, Reporting and Conformance (DMARC). These mechanisms provide authorization and specify policies to block forgeries.
Although the poor reputation of the IP spoofing your domain does not directly affect your IP, implementing DMARC can enhance your domain’s reputation against spoofing attempts.
Regarding the association between the IP address and our hostname, it is likely populated by passive DNS, which are searchable DNS resolver logs. However, it is important to note that the IP in question does not have a PTR record, and the hostname only resolves to our own IP, resulting in a mismatch.
In conclusion, understanding the nature of suspicious IP addresses and mail spoofing attempts is crucial for maintaining a secure email communication environment. By implementing proper authentication mechanisms and staying vigilant, we can protect our domain’s reputation and mitigate future incidents.
Disclaimer: This article is written by an employee of Cisco Talos, but the views expressed here are the author’s own and do not represent the company.