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Visionary Support Knowledge Base
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I cannot receive email from a certain sender?

Problem: A certain sender is trying to send you email, but it's being blocked by Visionary's servers. The sender is receiving a bounce-back message that says something similiar to the following:
  • 554 5.7.1 Service unavailable; Client host [] blocked using; Blocked - see
A bounce message like this is caused by the sender's mail server being listed in one of the several DNS blacklists we use.

What are these "DNS blacklists"?
There are several organizations that maintain DNS blacklists for ISPs to use as an effort to reduce spam to their customers. These organizations have several mail servers that monitor for spam activity from other mail servers on the internet. When they find a server that has been sending spam, they list that server in their blacklist. ISPs (such as Visionary) can then query these organizations each time a message is received to make sure the sender's mail server is not one that has been listed. In the example above, the oganization is So even though our servers are rejecting the mail, we are only doing so because they are listed in one of these blacklists that are not maintained by us.

Why are they listed in the DNS blacklist? I know they're not spammers!
Sometimes legitimate servers will end up on a blacklist by one or more of these organizations. The exact reason their mail server was listed is usually found in the bounce message, but if not then it's likely because their mail server had spam pass through it. The spam was probably sent from one of their user's computers that had a virus/worm and was NOT intentional.

Even though these blacklists can be frustrating when a legitimate mail server is listed, they are extremely effective and reject over 50% of the spam we receive (which is about 2.5 million msgs per day).

Solution: In order for them to be able to send mail to you again, you/they will need to request removal from the organization that has them listed in the blacklist. There is usually a URL in the bounce message (in the example above, the URL is: that you can go to that will give you more information about why they're listed and usually have a form to request that the mail server be removed. Some organizations will remove them without question upon request, and others will have to review it first. If they ask for an IP address, that is a series of numbers that can be found in the bounce message right after the "Service unavailable; Client host" and between the brackets [ and ]. In the example above, the IP address is

If you're having any trouble delisting the mail server, then we can whitelist them on our servers so that they can send to us regardless of blacklists they're listed on. Please send the IP address of the mail server and a short explanation to Please only do this if you've tried and failed to delist them from the organization that has them listed.


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