Implement SMTP Receive Support in Bridge46

[xlmnxp]

As part of our ongoing efforts to enhance the capabilities of Bridge46, we need to add support for the SMTP (Simple Mail Transfer Protocol) protocol. This will allow Bridge46 to handle email-related tasks, such as receiving emails, and integrating with existing email services.

The main tasks for this ticket include:

1. Research and evaluate SMTP implementation options for Bridge46 (e.g., using a library like Rust's samotop package or an external SMTP server).
2. Modify Bridge46 to support SMTP functionality, including the ability to receive emails.
3. Implement the necessary logic to handle SMTP commands, manage email queues, and integrate with external email services (if required).
4. Write extensive tests to ensure the SMTP functionality is working as expected, including edge cases and error handling.
5. Update the documentation and deployment procedures to reflect the new SMTP capabilities in Bridge46.
6. Perform thorough testing and validation to ensure the SMTP implementation does not impact the existing functionality of Bridge46.

Acceptance Criteria:

• Bridge46 can successfully receive emails using the SMTP protocol.
• The SMTP implementation is well-integrated with Bridge46's existing features and does not introduce any performance regressions.
• Bridge46 can handle common SMTP commands and gracefully handle errors or edge cases.
• The SMTP functionality is thoroughly documented, and the deployment process is updated accordingly.
• All tests pass, and no regressions are introduced in the existing functionality.