Title: "IMAP Connection Error: 'Socket error: 0x02: Connection not allowed by ruleset' when using SOCKS5 Proxy in Python"

Question

I'm trying to connect to an IMAP server through a SOCKS5 proxy using Python. However, I keep encountering the error: Socket error: 0x02: Connection not allowed by ruleset. Below is the code I'm using:

import imaplib
import socks
import socket
import ssl
import requests
from requests.auth import HTTPProxyAuth

# Proxy configuration
PROXY_HOST = "178.xx.xx.xxx"
PROXY_PORT = 10300
PROXY_USERNAME = "xxx"
PROXY_PASSWORD = "xxx"

# Email configuration
IMAP_SERVER = "imap.gmx.com"
IMAP_PORT = 993
EMAIL = "uhnwlwnosnyu@gmx.com"
PASSWORD = "xxxxx"

def check_proxy_connection():
    session = requests.Session()
    session.proxies = {
        "http": f"http://{PROXY_USERNAME}:{PROXY_PASSWORD}@{PROXY_HOST}:{PROXY_PORT}",
        "https": f"http://{PROXY_USERNAME}:{PROXY_PASSWORD}@{PROXY_HOST}:{PROXY_PORT}"
    }
    try:
        response = session.get("http://api.myip.com", timeout=10)
        response.raise_for_status()
        return response.json()
    except requests.RequestException as e:
        print(f"An error occurred: {e}")
        return None

# Check the proxy connection
proxy_response = check_proxy_connection()
if proxy_response:
    print(f"Proxy is working. Response from api.myip.com:\n{proxy_response}")
else:
    print("Proxy is not working. Exiting the script.")
    exit()

# Set up the proxy with authentication
socks.set_default_proxy(
    socks.SOCKS5,
    PROXY_HOST,
    PROXY_PORT,
    username=PROXY_USERNAME,
    password=PROXY_PASSWORD
)
socket.socket = socks.socksocket

try:
    # Create an SSL context
    ssl_context = ssl.create_default_context()

    # Connect to the IMAP server through the proxy
    imap_client = imaplib.IMAP4_SSL(IMAP_SERVER, IMAP_PORT, ssl_context=ssl_context)

    # Login to the email account
    imap_client.login(EMAIL, PASSWORD)
    print("Successfully logged in")

    # List available mailboxes
    status, mailboxes = imap_client.list()
    if status == 'OK':
        print("Available mailboxes:")
        for mailbox in mailboxes:
            print(mailbox.decode())

    # Select the inbox
    imap_client.select('INBOX')

    # Search for emails
    status, messages = imap_client.search(None, 'ALL')
    if status == 'OK':
        message_numbers = messages[0].split()
        print(f"Number of emails in inbox: {len(message_numbers)}")

        # Fetch the latest email
        if message_numbers:
            latest_email_id = message_numbers[-1]
            status, msg_data = imap_client.fetch(latest_email_id, '(RFC822)')
            if status == 'OK':
                print("Latest email fetched successfully")
                # Here you can process the email content if needed
                # raw_email = msg_data[0][1]
                # email_message = email.message_from_bytes(raw_email)
                # ...

except imaplib.IMAP4.error as e:
    print(f"An IMAP error occurred: {e}")
except Exception as e:
    print(f"An unexpected error occurred: {e}")
finally:
    try:
        imap_client.logout()
        print("Logged out and closed the connection")
    except Exception as e:
        print(f"Failed to close the connection cleanly: {e}")

Error Message: An unexpected error occurred: Socket error: 0x02: Connection not allowed by ruleset

Steps I've Taken:

Verified that the proxy works by checking the response from http://api.myip.com.
Attempted to connect to the IMAP server through the proxy using imaplib.IMAP4_SSL.

Environment:

Python version: 3.12.3
pysocks library for proxy handling
IMAP server: imap.gmx.com
Proxy: SOCKS5 with authentication

What could be causing the "Connection not allowed by ruleset" error when connecting through the SOCKS5 proxy? Are there any additional steps I need to take to properly configure the proxy for IMAP connections?