Stalwart Proxy is a multi-protocol e-mail migration proxy. It sits in
front of one or more mail backends and decides, per account, which
backend a connection belongs to. It terminates IMAP, POP3, ManageSieve,
SMTP submission, SMTP/LMTP and HTTP (JMAP) sessions, identifies the
account from the credentials the client already presents, replays the
authentication to the assigned backend and bridges the session, so no
client reconfiguration is required.

It is intended for migrating from legacy servers such as Dovecot or
Cyrus to Stalwart one mailbox at a time, for migrating between Stalwart
versions, and as a cache-locality router in front of a Stalwart cluster.
Account mappings can be stored in a flat file, Redis, PostgreSQL, MySQL,
or SQLite. The proxy is written in Rust.
