SMTP Recipients Refused: 'Too many protocol errors' - How to Fix

The error message 'SMTPRecipientsRefused: {'nan': (421, b'4.7.0 Too many protocol errors (6) on this connection, closing transmission channel.')}' typically indicates that the SMTP server has closed the transmission channel due to an excessive number of protocol errors during the connection. Here's how to troubleshoot and resolve this issue:

1. Check Your Network Connection: Ensure a stable and uninterrupted internet connection. A faulty or unstable network can cause protocol errors.

2. Verify Email Settings: Double-check your SMTP server settings, username, and password for accuracy.

3. Try a Different SMTP Server: Occasionally, SMTP servers experience issues that prevent email delivery. Switching to a different SMTP server may resolve the problem.

4. Increase Sending Intervals: Sending a large volume of emails within a short timeframe can trigger spam filters and lead to protocol errors. Increase the time interval between sending emails or reduce the number of emails sent at once.

5. Consider Shared Server Issues: If using a shared SMTP server, other users' activity may contribute to protocol errors. Contact your email service provider to upgrade to an independent SMTP server or adjust shared server usage patterns.

If the above steps don't address the issue, reach out to your email service provider for further assistance in reviewing your email settings and the SMTP server.