Backup and Gateway

Summary

This article addresses common email delivery issues and how to resolve them, including port 25 accessibility, firewall configurations, and spam filtering for DuoCircle services.

The article provides troubleshooting steps for users experiencing email delivery issues and addresses common configuration errors related to email servers and gateways. It also explains how DuoCircle's services, such as Backup MX and Email Forward, can enhance spam filtering, prevent message delays, and handle specific issues with blacklisting and greylisting. The article includes instructions for configuring MX records to prevent spam and offers tips for Barracuda Spam Firewall users. 

Key issues like port forwarding, email acceptance, and the use of aliases are covered.

Objective

By following this guide, you will troubleshoot email delivery issues, manage MX records, and set up effective spam filtering.

Introduction

If you’re experiencing problems receiving emails, several factors may be causing delivery failures. This guide provides troubleshooting steps to ensure your email server and network settings are configured correctly, including guidance on port forwarding, firewall settings, and domain configuration. Additionally, it covers how DuoCircle’s Backup MX service helps with spam filtering and virus elimination.

Prerequisites

• Access to your email server and logs.
• Firewall and router configuration access.
• Knowledge of your domain’s MX records.

Step-by-Step Instructions

1. Check Server Accessibility on Port 25
   Ensure your email server is reachable on port 25 by using the following command:

   telnet domain.com 25

2. Review Firewall Settings
   Ensure that your firewall isn’t blocking DuoCircle’s servers. The necessary IP address blocks to whitelist are listed here.
3. Verify Router Port Forwarding
   Check your router's configuration to ensure it is forwarding port 25. More information on port forwarding can be found here.
4. Check Email Acceptance
   Ensure your server is accepting emails for the correct user and domain. Your server logs will indicate if the emails are being rejected and provide the reason.
5. Verify Email Gateway Settings
   Make sure the destination server field for Email Gateway is correctly configured and points to the proper hostname, resolving to your Email server.

Barracuda Spam Firewall Users

If you are using Barracuda Spam Firewall, ensure you add DuoCircle’s IP addresses under the Trusted Forwarder IP section. This will allow Barracuda to continue scanning email content while preventing our servers from being blacklisted.

Contacting DuoCircle Support

If you encounter email delivery issues, contact DuoCircle support. Provide the “To” and “From” addresses, along with the time and timezone for an email you didn’t receive. This will help us trace logs and diagnose the issue.

Spam and Filtering with DuoCircle Backup MX

DuoCircle Backup MX provides an email backup solution that includes spam and virus scanning.

Configuring MX Records to Prevent Spam

To reduce spam, you can configure your MX records in a primary-secondary-primary setup. Spammers often target the lowest-priority MX record to bypass anti-spam filters. Here’s an example configuration:

Forwarding

Mail delivery problems are often hard to diagnose due to various potential issues. Follow these steps to resolve common email forwarding issues. If unresolved, you can contact support for further assistance.

Mail Delay Due to Greylisting

If your emails are delayed and arrive in batches, this could be a result of greylisting. Contact your mail provider to whitelist DuoCircle’s legitimate mail. You can also notify support with full email headers of delayed messages for further investigation.

550 User Unknown Error

DuoCircle Email Forward will not reject email unless a 5xx Permanent Failure error is received from the destination server. A common cause is blacklisting. Contact your email provider to remove the blacklist and reach out to support with full email headers of rejected messages.

Queue Size and Message Limits

DuoCircle Email Forward doesn’t limit the total volume of individual messages but does have a per-message size limit of 50MB. Messages exceeding this will be returned to the sender.

FAQs

Can DuoCircle Email Forward block more spam?

Yes, DuoCircle Email Forward includes anti-spam options that can significantly reduce the amount of spam reaching your inbox.

Can I use a third-party anti-spam service with DuoCircle Email Forward?

No, it’s not possible to use DuoCircle Email Forward simultaneously with another anti-spam service like Postini.

Why is spam scanning enabled on some aliases?

Certain email hosting providers are more sensitive to mail delivery issues. Spam scanning and virus elimination are automatically enabled for specific recipient domains to ensure proper delivery.

Can I create wildcard aliases?

No, due to security risks like dictionary attacks, wildcard or “catch-all” aliases are no longer supported in DuoCircle Email Forward.