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Open Relay and Blacklist - Open relay means that anyone can make use your mail server - usually by spammers to send junk email via your email server to hundred of thousands of recipients.
MX records or Mail Exchangers
Reasons for undeliverable mails
Open Relay and blacklist
Mail Servers FAQs
If you are using your own mail server program to send emails the most common problems for undeliverable mails are identified here, please go through them carefully and it will solve most of your problems.

ORDB (Open Relay Database) a non-profit organization that maintains database of open relay SMTP servers by listing servers IP addresses individually.


Open relay are servers allowing anyone to send mails to any destination, therefore, are considered potential sources of spam.

Notes: It is not your or ISPs mail server that gets blacklisted, it is your email domain IP address or the entire block of IP address maintained by your ISPs.

How to check if your email domain is blacklisted?
One way to tell if you have a problem is to find the IP address of the e-mail server and do a Spam Database Lookup. See: Meaning of spam

Notes: Sometimes a never-before-used, dedicated IP address maybe blacklisted because it is part of a block of IP addresses assigned to an ISP which has been accused of spamming.

You can check it out whether your email domain or ISPs mail server is on the blacklist at below sites, follow the site instructions and you will get an immediate report...
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Guest Book  |  Minute Wisdom
Filled with stolen moments, lost dreams, and too many 'if only'
  or A new web-based forum for getting help is available at: or

You can monitor some of the most widely-used blacklist at
MAPS Realtime Blackhole list
At Google yourself here...

Enable SMTP authentication

If your mail server is not enabled for SMTP authentication (to protect it from unauthorized users)--it can become an open relay by allowing anyone on the Internet to (relay) send mail to any destination--resulting in your domain IP address being blacklisted--meaning that; all your emails will be deleted or blocked from ISPs mail servers using ORDB database or other organizations maintaining open relay database.

To be removed from their blacklist, you need to stop being open relay (by enabling SMTP Authentication on your mail server) and submit your server domain IP address to ORDB for testing. As soon as your serve is verified to be no longer an open relay, you will be removed from their database.

After being removed from their blacklist, you may find that your emails are still blocked or deleted by other ISPs; the reason is that your IP address may also be blacklisted by a few other organizations that maintain a database of open relays.

are another non-profit organization that maintains a database of open relay servers. MAPS sometimes lists an entire ISPs dial-up IP addresses--meaning that if you are sending mails with an IP address within the blacklisted list, your emails are filtered and deleted. And it is not easy to be removed from MAPS database list.

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Art of War - "Leaders  without strategy of warfare, invite defeat." for more information about MAPS and other non-profit anti-spam organizations that provides DNS based service that verify open relays mail servers;
  • LLC Mail Abuse Prevention System
  • RBL Realtime Blackhole List
  • DUL DialUp Access List
  • RSS Relay Spam Stopper.   

Other organizations maintaining database of open relay servers and blacklisted sites:

  • A new web-based forum for getting help is available at:

About Open Relay, blacklist and spammers
Open relay means that anyone can make use your mail server - usually by spammers to send junk email via your email-server to hundred of thousands of recipients.

Open Relay, blacklist and spammers

Sending a group of emails to ISPs mail server that are not personally addressed in the To: or CC: field, to the recipients by using the BCC: field usually result in having your emails blocked, deleted, as well as having your email IP domain blacklisted (open relay).

Now-a-days, ISP doesn’t bother to bounce them and won't inform you that your mails are undeliverable. Therefore, your emails may seem to be accepted but in reality they were not.


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The reason is that, when email addresses are entered into the BCC: field, recipients cannot see the email address, so does the receiving mail server (that's part of the how the filtering process detects them).

But to send email(s), an email address have to be entered into the To: field, for recipients to see, for example:
To: myfriends_@_mymailsserver and that's exactly what your recipients will see in their mail reader To: field.




Since your email is not personally addressed to each and every recipient, a mail server that received such email may automatically filter and identify it as SPAM, delete it, and/or may blacklist the sender email domain.

The reason are that, to the sender, sending 100 emails using the BCC: field gives the impression that he or she is sending only one message by BCC: to a 100 others.

But the effect for the mail server, is actually equivalent to 100 different email messages sent to 100 different email addresses--because the mail server have to make a 100 duplicate copies of the message before they can be delivered out, to each of the 100 BCC: recipients.

Some ISPs do not mind if you send about 50 BCC messages on a daily basis -- policy may differ from one ISP to another, therefore it is better to check it-out before your account get terminated.

When too many account holders are sending emails using BCC: the ultimate effect is total congestion at the mail server and therefore, degrading its performance--Meaning that you are using their (ISPs) resources and ISPs administrator view it with disdain, hence, account holders using BCC: to send large quantities of emails will have their account terminated (that's how spammers make used of open relay servers to spam).

Open relays easily detected by ISP mail serves filtering the BCC: field, which is the most favored method used by spammers to send hundreds (millions) of thousands emails with just one email message--otherwise they will have to send each email one by one, addressing each recipient by the To: field and having to maintain their own expensive high speed mail servers--which would limit their spamming activities.

Spammers uses SMTP Relay Check tool to probe SMTP mail server--although, an insecure (open relay) mail server may not be what it seems to be--because mails accept may in actual fact were dumped (deleted). And the only way to be sure that the mail server is an open relay, is to send (relay) an email back to yourself.

Important: SMTP Relay Checker probe tools--(available from trigger an intruder alarm and will alert the system administrator of a hacker probing--which is illegal--your IP address, date and time of probe will be automatically record and you can be subjected to law suits.

A new web-based forum for getting help is available at