added dovecot imap proxy

README.md

@@ -1 +1,34 @@
-# imap-proxy
+# Dovecot IMAP Proxy
+
+Dovecot deployment acting as a pure IMAP proxy: it listens on your hostname (e.g. `imap.example.com`) with its own SSL certificate, accepts and terminates the client connections (implicit TLS on 993, STARTTLS on 143), then connects to the destination server (e.g. `imap.example.net`) as if it were the client, over the destination's own SSL, and forwards the traffic bit-by-bit in both directions.
+
+## How it works
+Dovecot's login proxy is used with a `static` passdb: any username is accepted, no password is verified locally (`nopassword`), and the login is forwarded (credentials included) to the destination host, which performs the real authentication. Once the remote login succeeds, dovecot becomes a dumb pipe between client and destination. No mail is ever stored locally.
+
+Because the password must be forwarded, clients have to use cleartext mechanisms (`PLAIN` / `LOGIN`); dovecot only allows them after TLS is negotiated, so nothing travels unencrypted.
+
+## Configuration
+Copy `example.env` to `.env` and adjust:
+- `SSL_CERT` / `SSL_KEY`: certificate and key for the hostname the proxy serves (e.g. Let's Encrypt live paths).
+- `IMAP_EXPOSE` / `IMAPS_EXPOSE`: host bindings for ports 143/993.
+
+Copy `example.dovecot.conf` to `${DOVECOT_CONF}` (default `./data/dovecot.conf`) and set `host` in the `passdb static` block to your destination server. The destination certificate is verified against the system CA bundle (`ssl_client_ca_file`); use `ssl = any-cert` instead of `ssl = yes` if the destination has a self-signed certificate.
+
+## Usage
+```sh
+cp example.env .env
+mkdir -p data && cp example.dovecot.conf data/dovecot.conf
+$EDITOR .env data/dovecot.conf
+docker compose up -d
+```
+
+## Testing
+```sh
+openssl s_client -connect imap.example.com:993 -quiet
+# then login as an existing user on the destination server:
+a LOGIN user@example.com password
+b LIST "" "*"
+```
+
+## Notes
+The `-root` image flavor is used so dovecot can read certificates that are only readable by root (as the Let's Encrypt live folder is); dovecot itself still drops privileges per-service. If your certificates are world-readable you can drop the `-root` suffix from `DOVECOT_VERSION`.