I would like to kindly request the addition of the Sieve vacation extension (RFC 5230) to Proton Mail’s implementation.

This extension would allow users to create personalized automatic replies directly via Sieve filters, for example:

Sending a confirmation email when a message is received on a specific address (e.g., support or contact mailbox).

Customizing the subject and body of the automatic response.

Ensuring rate limits with the :days parameter to avoid mail loops.

Currently, Proton Mail only provides a global autoresponder via the settings panel, which does not allow for conditional or address-specific replies. Implementing the vacation extension in Sieve would give users far greater flexibility and security, especially for domains used in professional or business contexts.