Keywords are special words or phrases. Add related keywords to a keyword list to identify specific types of data. For example, "prognosis", "blood type", "vaccination", and "physician" are keywords that may appear in a medical certificate. To prevent the transmission of medical certificate files, configure IMSS to block files containing these keywords.

Expressions are data that have a certain structure. For example, credit card numbers typically have 16 digits and appear in the format "nnnn-nnnn-nnnn-nnnn", making them suitable for expression-based detections.

IMSS can take action on a message based on the content of its subject, body, or header. To filter messages by content, combine keywords or regular expressions in keyword expression lists.