Synology NAS Error Code 63: How to Fix It

Medium 20-45 minutes Medium Severity Verified June 2026
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Error Code
63
Brand
Synology
Product Type
nas
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
20-45 minutes
Synology NAS Error Code 63 indicates that the DSM Mail Server failed to relay outgoing emails through the configured SMTP server. This typically happens when your SMTP credentials, server settings, or network configuration are incorrect or blocked. Fixing this error restores email notifications for system alerts, backup reports, and other DSM communications.
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Tools You'll Need

How to Fix Error Code 63

  1. Check Your SMTP Server Settings

  2. Verify Your SMTP Username and Password

    Do not use your main account password if two-factor authentication (2FA) is enabled on your email account. Always use an App Password in that case.

  3. Test SMTP Port Connectivity

    Only enable SSH temporarily for diagnostics. Disable it again when finished to reduce security exposure.

  4. Check Firewall and Router Settings

  5. Review DSM Mail Server Package Configuration

  6. Check Email Provider Security Restrictions

  7. Send a Test Email and Review Logs

  8. Consider Using a Dedicated SMTP Relay Service

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When to Call a Professional

Contact Synology support or a network administrator if you have confirmed correct SMTP credentials and port access but the error persists, especially in a corporate or enterprise environment where email routing may be governed by internal IT policies or Exchange Server configurations you cannot modify yourself. If your NAS is managed by an IT department, relay the error code and log details to them for assisted resolution.

Frequently Asked Questions

What does Synology Error Code 63 mean?
Error Code 63 on a Synology NAS means the DSM Mail Server failed to relay outgoing email through the configured SMTP server. This prevents DSM from sending system alerts, backup notifications, and other email messages.
Why is my Synology NAS not sending email notifications?
Your Synology NAS may not be sending email notifications due to incorrect SMTP server address or port, wrong username or password, ISP blocking of SMTP ports, email provider security restrictions (such as requiring an App Password), or a misconfigured firewall rule on your router or DSM itself.
How do I fix Gmail SMTP relay failing on Synology DSM?
To fix Gmail SMTP relay on Synology DSM, use smtp.gmail.com on port 587 with STARTTLS encryption. If your Google account has 2-Step Verification enabled, generate an App Password from your Google Account security settings and use that instead of your regular Gmail password in DSM's notification settings.
Which SMTP port should I use for Synology email notifications?
The recommended port for most providers is 587 using STARTTLS encryption. Port 465 with SSL/TLS is also commonly supported. Avoid port 25 as most ISPs block it for residential and small business connections. Check your specific email provider's documentation for the correct port.
Can I use a free SMTP relay service with my Synology NAS?
Yes. Services like SendGrid, Mailgun, and Amazon SES offer free or low-cost SMTP relay tiers that work well with Synology NAS. These are especially useful if your ISP blocks standard SMTP ports or if your email provider's security policies prevent third-party relay. Enter the service's SMTP credentials in Control Panel > Notification > Email.

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