Proton Mail's Sieve implementation is missing several powerful RFC-standard extensions that would unlock advanced email automation.

Here are the key missing features: Mailbox Creation and Checking (RFC5490, RFC9042) - Automatically create folders and organize emails by sender domain without manual setup.

Notifications (RFC5435/RFC5436) - Send SMS or email notifications when specific emails arrive instead of just filing them.

Body Content Filtering (RFC5173) - Filter emails based on message body content, not just headers, for smarter spam detection.

Edit Headers (RFC5293) - Modify or add custom headers to emails as they arrive.

File Carbon Copy (RFC8580) - Keep automatic copies of filtered emails in specific folders for compliance or backup.

Calendar Processing (RFC9671) - Automatically handle calendar invitations and ICALENDAR attachments.