Mail services relay messages across both the Internet and private networks. Adversaries often use the channels formed by mail protocols to target internal systems. This chapter details the tactics you can adopt to identify flaws in available mail services—including service identification, enumeration of enabled options, and testing for known weaknesses.
Mail Protocols
Table 9-1 lists mail services supporting mail delivery (via SMTP) and collection (via POP3 and IMAP). TLS is often used to provide transport security.
Table 9-1. Mail protocols detailed in this chapter
Port
Protocol
TLS
Name
Description
Hydra
TCP
UDP
25
●
–
–
smtp
Simple Mail Transfer Protocol
●
465
●
–
●
smtps
587
●
–
–
submission
110
●
–
–
pop3
Post Office Protocol
●
995
●
–
●
pop3s
143
●
–
–
imap2
Internet Message Access Protocol
●
993
●
–
●
imaps
SMTP
SMTP servers (known as message transfer agents or MTAs) transport email using software packages such as Sendmail and Microsoft Exchange. Figure 9-1 demonstrates a typical configuration, in which content filtering mechanisms are used to scrub email.
Figure 9-1. SMTP servers processing Internet-based mail
In this case, inbound mail is first sent to a managed security service provider (MSSP) to quarantine malware, spam, and other threats. The MSSP relays processed mail to the organization’s ...
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