Hello Proton Mail Bridge Team,

I would like to request support for applying Proton Mail labels via IMAP.

Currently, the Bridge exposes labels as IMAP folders (e.g., Labels/Paperless), but it does not support any IMAP mechanism for applying a label to a message.

This creates a limitation:
- When a user labels an email in Proton Mail, the Bridge shows it in both INBOX and the label folder (virtual projection).
- When an IMAP client moves a message into Labels/<Label>, the message is removed from INBOX instead of receiving the label.
- There is no IMAP command available to apply a label while keeping the message in INBOX.

To enable proper interoperability with IMAP clients that support tagging workflows (e.g., Paperless‑NGX, mail processors, automation tools), it would be extremely helpful if the Bridge implemented an IMAP‑level label mechanism.

Two possible approaches:
1. Implement Gmail’s IMAP label extension (X‑GM‑EXT‑1)
This would allow clients to use:
STORE <UID> +X-GM-LABELS ("Paperless")
and would align Proton Mail with the de‑facto standard for IMAP label support.

1. Provide a Proton‑specific IMAP extension For example: STORE <UID> +X-PM-LABELS ("Paperless") This would allow IMAP clients to apply Proton labels without changing folder membership.

Why this matters
- Many automation tools rely on IMAP label support to mark processed emails.
- Without label support, IMAP clients must MOVE messages, which changes the folder instead of applying a label.
- This breaks workflows where messages should remain in INBOX but also receive a label.

Adding IMAP label support would significantly improve compatibility with modern mail automation tools and make Proton Mail Bridge more predictable for IMAP clients.

Thank you for considering this enhancement.