Attachment filtering is a mail-security control that inspects incoming files and blocks or quarantines risky ones before they reach a user’s inbox. It can use file type rules, reputation checks, content inspection, sandboxing, and policy controls to decide whether an attachment is allowed.
This matters because email attachments are a common delivery path for phishing, malware, and file-type masquerading. An attachment may pretend to be a harmless document, archive, or font file while actually carrying a harmful payload or a dangerous link to one. Good filtering reduces the chance that a user ever sees the lure, which is often the strongest defense. In practice, defenders tune rules for executable files, macros, script content, and unexpected formats, then add extra scrutiny for attachments that do not match the sender, message context, or business workflow.