Synology NAS Mail Server Bounce Error: How to Fix It

Medium 2-4 hours plus 24-48 hours DNS propagation Medium Severity Verified June 2026
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Error Code
Mail server bounce
Brand
Synology
Product Type
nas
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
2-4 hours plus 24-48 hours DNS propagation
The Synology mail server bounce error occurs when your outgoing emails are rejected by recipient servers due to misconfigured DNS authentication records. This typically involves problems with SPF, DKIM, or PTR records that verify your domain's legitimacy as an email sender.
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Tools You'll Need

How to Fix Error Code Mail server bounce

  1. Access Synology DSM and MailPlus Server

  2. Check Email Bounce Logs

  3. Verify SPF Record Configuration

    Incorrect SPF records can cause all emails to be rejected. Test changes with email testing tools before implementing.

  4. Configure DKIM Authentication

  5. Set Up PTR (Reverse DNS) Record

  6. Configure DMARC Policy

  7. Test DNS Propagation

  8. Send Test Emails

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When to Call a Professional

Contact a network administrator or IT professional if you don't have access to DNS management, ISP PTR record configuration, or if bounce errors persist after proper DNS configuration. Professional help is also recommended for business-critical email systems.

Frequently Asked Questions

Why do my Synology emails keep bouncing back?
Email bounces typically occur when receiving servers can't verify your domain's authenticity through SPF, DKIM, or PTR records. Missing or incorrect DNS authentication records cause recipient servers to reject your emails as potential spam.
How long does it take for DNS changes to fix email bouncing?
DNS propagation typically takes 24-48 hours globally. However, some changes may be effective within a few hours. Test your configuration periodically using DNS lookup tools to monitor propagation progress.
Can I fix Synology mail bounces without technical knowledge?
Basic DNS record configuration requires some technical understanding. If you're uncomfortable editing DNS records or lack access to domain management, consider hiring a network administrator or IT professional to ensure proper configuration.
What's the difference between SPF, DKIM, and DMARC records?
SPF authorizes IP addresses to send emails for your domain. DKIM adds cryptographic signatures to verify message authenticity. DMARC provides policy instructions for handling emails that fail SPF or DKIM validation.
Why is my PTR record important for email delivery?
PTR records provide reverse DNS lookup, allowing receiving servers to verify that your IP address legitimately corresponds to your domain. Missing PTR records are a common cause of email delivery issues and spam filtering.

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