Hotmail has strict anti-SPAM policies using SmartScreen, a program developed by Microsoft, to scan and classify incoming emails. Hotmail limits the number of emails sent from a single IP based on its reputation. Exceeding this limit results in SMTP error code 421.

Anti-SPAM Policy:

1. No fake addresses or deceptive content.
2. No nonexistent domain names.
3. No hiding information about the email's path.
4. No sending misleading emails.
5. No subject lines that don't match the email content.
6. No bulk emails to unsubscribed users.
7. No fraudulent emails or phishing.

Sending Guidelines for Marketers:

1. Handle complaints and provide unsubscribe links.
2. Ensure email addresses for complaints work efficiently.
3. Follow through on promises like refunds or product exchanges.
4. Use accurate information and subject lines.
5. Clearly state if the email is an advertisement.
6. Provide your detailed address and contact methods.
7. Explain how to unsubscribe from your mailing list.

Improving Delivery:

• Place an unsubscribe link prominently.
• Address complaints and remove unsubscribed emails.
• Remind recipients of their subscription.
• Validate your email list to avoid sending to inactive addresses.