Procmail
Procmail is a mail processing utility for Unix-like systems that filters and sorts incoming email messages based on user-defined rules. It operates as a local delivery agent (LDA) that integrates with mail transfer agents (MTAs) like Sendmail or Postfix to automatically organize, forward, or discard emails. It is known for its powerful rule-based configuration, allowing users to create complex filtering logic using recipes in a .procmailrc file.
Developers should learn Procmail when managing email servers or automating email workflows in Unix environments, such as for spam filtering, sorting emails into folders, or triggering scripts based on incoming messages. It is particularly useful for system administrators, DevOps engineers, or developers building applications that require server-side email processing, as it provides a lightweight, scriptable solution without relying on external services. However, it is less relevant for modern cloud-based email systems, where tools like Sieve or integrated filtering in services like Gmail are more common.