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.

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.