Software Secure Firewall Threat Defense
Platform Secure Firewall Threat Defense Virtual
Activity Onboard

Advanced Network Analysis and Preprocessing Application Layer Preprocessors The IMAP Preprocessor

Last updated: Jul 29, 2025

The IMAP Preprocessor


 

This section applies to Snort 2 preprocessors. For information on Snort 3 inspectors, see https://www.cisco.com/go/snort3-inspectors.

The Internet Message Application Protocol (IMAP) is used to retrieve email from a remote IMAP server. The IMAP preprocessor inspects server-to-client IMAP4 traffic and, when associated preprocessor rules are enabled, generates events on anomalous traffic. The preprocessor can also extract and decode email attachments in client-to-server IMAP4 traffic and send the attachment data to the rules engine. You can use the file_data keyword in an intrusion rule to point to the attachment data.

Extraction and decoding include multiple attachments, when present, and large attachments that span multiple packets.