Fixing the "Error 501 b'5.5.4 Invalid domain name'" in WSL Ubuntu

Based on your screenshots and description, I can see you're encountering a domain name validation error when trying to send emails through Outlook from WSL Ubuntu, while the same code works fine on Windows.

The Problem

The error 501 5.5.4 Invalid domain name typically occurs when the SMTP server rejects the domain part of an email address because it doesn't conform to proper domain name standards.

Looking at your code, I can see you're using:

• SMTP server: smtp-mail.outlook.com
• Port: 587
• Email: projectsoftwareengineering2024@outlook.com

Likely Causes and Solutions

1. Hostname Configuration in WSL

WSL might not have a properly configured hostname or FQDN (Fully Qualified Domain Name), which Outlook's SMTP server is rejecting.

Try setting a proper hostname in your WSL environment:

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sudo hostnamectl set-hostname your-hostname.local

Then edit your /etc/hosts file to include this hostname:

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sudo nano /etc/hosts

Add or modify the line with your local IP:

127.0.0.1   localhost your-hostname.local

2. SMTP HELO/EHLO Command Issue

The error might be related to how your SMTP client identifies itself to the server. Try explicitly setting the local hostname in your email sending code:

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server = smtplib.SMTP('smtp-mail.outlook.com', 587)
server.ehlo('your-hostname.local')  # Add this line
server.starttls()
server.ehlo('your-hostname.local')  # And this one after TLS

3. Email Configuration

Ensure your from_email and to_email variables have valid domain parts. Based on your screenshots, check that:

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from_email = 'projectsoftwareengineering2024@outlook.com'  # Verify this is correct

4. Network Configuration

WSL's network configuration might be affecting how it communicates with external SMTP servers. Try:

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sudo apt update
sudo apt install resolvconf

Then configure proper DNS resolution.

Alternative Approach

If the above solutions don't work, consider using Django's built-in email functionality with proper settings in your settings.py:

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EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'
EMAIL_HOST = 'smtp-mail.outlook.com'
EMAIL_PORT = 587
EMAIL_USE_TLS = True
EMAIL_HOST_USER = 'projectsoftwareengineering2024@outlook.com'
EMAIL_HOST_PASSWORD = 'your-password'
DEFAULT_FROM_EMAIL = 'projectsoftwareengineering2024@outlook.com'

Then send emails using Django's send_mail function instead of directly using smtplib.