A simple smtps, imaps proxy server

mail_proxy.py

#!/usr/bin/env python3

# support python 3.5 or later, use python standard library only

import asyncio
import ssl


async def dial(client_conn, server_conn):
    async def io_copy(reader, writer):
        while True:
            data = await reader.read(32)
            if not data:
                break
            writer.write(data)
        writer.close()

    asyncio.ensure_future(io_copy(client_conn[0], server_conn[1]))
    asyncio.ensure_future(io_copy(server_conn[0], client_conn[1]))


async def handle_smtp_connection(reader, writer):
    server_conn = await asyncio.open_connection(
        # you can change the dest smtp server hostname
        host="smtp.yandex.ru",
        port=465,
        ssl=ssl.create_default_context(),
    )
    asyncio.ensure_future(dial((reader, writer), server_conn))


async def handle_imap_connection(reader, writer):
    server_conn = await asyncio.open_connection(
        # you can change the dest imap server hostname
        host="imap.yandex.ru",
        port=993,
        ssl=ssl.create_default_context(),
    )
    asyncio.ensure_future(dial((reader, writer), server_conn))


def main():
    loop = asyncio.get_event_loop()
    ssl_ctx = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
    # load your domain's ssl certificate
    # recommend let's encrypt
    ssl_ctx.load_cert_chain('ssl.crt', 'ssl.key')
    smtp_server = asyncio.start_server(
        handle_smtp_connection,
        host='0.0.0.0',
        port=465,
        ssl=ssl_ctx,
    )
    imap_server = asyncio.start_server(
        handle_imap_connection,
        host='0.0.0.0',
        port=993,
        ssl=ssl_ctx,
    )
    try:
        smtp_server = loop.run_until_complete(smtp_server)
        imap_server = loop.run_until_complete(imap_server)
        loop.run_forever()
    except KeyboardInterrupt:
        pass
    finally:
        smtp_server.close()
        imap_server.close()
        loop.close()


if __name__ == "__main__":
    main()