Backup and Gateway

  • If you are not receiving Email, you should first make sure your server is reachable on port 25; you can telnet to it using: telnet 25
  • If not reachable, check your firewall to make sure you are not blocking our servers. The IP address blocks to whitelist are listed here
  • Check that your router is forwarding port 25; you can find information about Port Forwarding here.
  • Make sure your server is accepting email for the user and domain you are sending to; your server logs will tell you if it is rejecting the mail we are trying to deliver, and why.
  • Make sure your destination server field for Email Gateway is pointing to the correct hostname, which should resolve to the IP of your Email server.

Barracuda Spam Firewall users: Please ensure that you add the following IP addresses under the Trusted Forwarder IP section for your device. This allows your Barracuda to continue scanning message content while ensuring our servers are not accidentally blacklisted.

If you need to contact DuoCircle for support with your email, please send us the To and From addresses, along with the time and timezone that an email was sent to you for one of the emails you didn’t receive. That will enable us to look through logs for you.

I’m getting a lot of spam. Can I block more of it with DuoCircle Email Backup MX?

DuoCircle Email Backup MX is an email backup solution that performs spam scanning and virus elimination.

You can also change your MX records to a primary-secondary-primary configuration. Many spammers automatically target the lowest-priority MX record by default to bypass the anti-spam filters on the primary mail server. To help prevent this, adding the primary MX again as your lowest-priority record will thwart this tactic:


Please Note: If you use the primary-secondary-primary configuration our MX checker is going to state that the settings are wrong, because the setting isn’t following the MX rule of the checker.


Mail delivery problems can often be difficult to troubleshoot, as there are many points along the way where a message could be delayed, rejected, or even silently dropped without the sender ever knowing a problem occurred. Please check the following entries to see if they describe your problem; if not, you can contact our support team for further help.

When contacting support, please send the full headers of any delayed or rejected emails (including timestamps and Received: entries) where available, and describe the time-frame of the problem to the nearest hour with timezone. Please make sure you contact support using an email address outside of the problem domain to make sure we can contact you!

Mail is delayed for hours, then arrives all at once.

This is a symptom of greylisting, where a mail server will temporarily reject mail (4xx error) to deter spammers. If your mail provider is greylisting DuoCircle Email Forward, you should contact them to let them know that the mail destined for your addresses is legitimate, and contact support to let us know of the problem. (Make sure to include the full headers of delayed messages so we can properly diagnose the issue.)

My mail is being rejected with a 550 User Unknown error.

Unless DuoCircle Email Forward explicitly receives a 5xx Permanent Failure error from the destination server, we will not reject email with this form of error. There are many potential causes of this problem, but one of the most common is blacklisting. Many email providers use blacklists or automated spam controls that block senders after too many “bad” messages. You will need to contact your provider and ask them to allow your mail to be delivered, then contact support to let us know of the problem. (Make sure to include the full headers of any rejected mail so we can properly diagnose the problem.)

I receive a lot of mail. What are the queue size and message size limits?

DuoCircle Email Forward does not limit the total volume of individual messages it can store or redeliver. DuoCircle Email Forward has a per-message size limit of 50MB; individual messages larger than 50MB (after encoding) will be returned to sender with a useful error message.

I’m getting a lot of spam. Can I block more of it with DuoCircle Email Forward?

DuoCircle Email Forward includes a variety of anti-spam options. By utilizing these features, you can drastically reduce the amount of spam delivered to your server via DuoCircle Email Forward. 

I want to use an anti-spam service like Postini as well as DuoCircle Email Forward.

Unfortunately, you cannot use DuoCircle Email Forward and a third-party anti-spam service simultaneously.

Some of my aliases automatically have spam scanning enabled. Why?

Some email hosting providers are more sensitive to mail delivery than others. In an effort to ensure smooth, consistent mail delivery to certain providers, some aliases will have spam scanning and virus elimination automatically enabled when they are created.

We currently force filtering for the following recipient domains:,,,,,,,,,,,,,,

Can I create Wildcard aliases?

Due to dictionary attacks and collateral spam problems, it is no longer possible to create a “default” or “catch-all” Wildcard alias in DuoCircle Email Forward.