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Explanation of error 550
Last Updated 11/24/2012 1:00 PM

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Explanation of error "550 5.0.0. ...blocked as possible open relay"
This error message means that an e-mail that you sent, or an e-mail that was forged to appear as if you had sent it, matched a filter on our e-mail servers. These filters were put in place to control the quantity of unsolicited commercial e-mail ("UCE" or "spam") sent to our customers. There are a number of reasons why a particular server or host may be included in our filter:
  • Open Relays

    Typically, a mail server is configured to allow anyone to send e-mail to local recipients, or to allow senders on that same network to send to anyone on the Internet. An "Open Relay" is a server that has been misconfigured in such a way that it allows anyone on the Internet to relay messages to anyone else on the Internet. This is bad because it allows spammers to relay UCE through the server with anonymity. In a properly configured mail server, the mail administrator can identify and take steps such as suspending or terminating the account of someone who abuses the e-mail service.

  • Open Proxies

    An "Open Proxy" is much like an open relay in that it allows spammers to send e-mails anonymously. However, while an open relay "listens" on the port used for e-mail traffic, an open proxy "listens" upon other ports, such as those used for web browsing. Also, unlike an open relay, an open proxy can be used for many other purposes besides relaying e-mail--for example, anonymous web browsing, port scanning, defacing web sites or other illegal activities.

  • Insecure or Improperly Secured FormMail Scripts

    FormMail is a script that allows visitors to a web site to send questions, feedback, or other communications to the owner or maintainer of that web site. Unfortunately, older versions of FormMail had security flaws that allowed spammers to send unsolicited e-mails through the web server that hosted the FormMail script.

  • Virus or Trojan Activity

    Many viruses, trojans and other malware have been written to operate in much the same way as open relays and open proxies, allowing spammers to relay UCE through an unsuspecting victim's computer. Computers compromised in this way are called "zombies" and are one of the biggest problems faced by Internet Service Providers today.

  • Deliberate Spamming

    Finally, there are those miscreants who abuse e-mail services intentionally by sending unsolicited commercial or bulk e-mails to literally thousands of recipients. Such practices place an extreme load upon the mail servers through which the offending e-mails are sent, and clutter the recipients' inboxes. Like many other ISP's, we blacklist any known or suspected spam sources in order to maintain our customers' good will and protect our mail servers.
If you wish to be removed from the filters on our e-mail servers, you must identify how the offending e-mail was sent through your server or computer, take action to resolve the problem, and contact our mail server administrators to request that we remove your server(s) from our filters. While we will evaluate all requests for removal, removal is at our sole discretion, and we are not under any obligation to comply with your request. You may reach us via e-mail at either or
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