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Email blacklisting

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Email blacklisting occurs when an email service provider puts another e-mail service provider on a "blacklist" and stops accepting email from that provider. This is usually done because it is perceived that a high volume of spam is coming from the blocked provider and its "reputation" is downgraded.

If you send an email to someone whose provider has blacklisted NCF mail you will generally get a message back that indicates that delivery was refused, such as:

This is the mail system at host mail.ncf.ca.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients...
The mail system...host mx1c9.megamailservers.com[] said ...Connection originating from an IP address with a poor reputation.

What causes blacklisting of NCF mail

Generally other e-mail providers blacklist NCF mail when they think that a high volume of spam is coming from NCF. This may actually be the case or it may be that a spammer is spoofing NCF IP addresses, in other words pretending that their spam mail is coming from NCF, when it isn't.

In most cases blacklisting of NCF occurs because one or more NCF members running Microsoft Windows have had their computers infected with a virus that grabs their address book and sends out spam to all their contacts. Their computer may also be part of a botnet and under remote control to send out large quantities of spam.

What can you do if your email gets bounced

The easiest solution is simply to wait.

Most large email service providers use commercial blacklisting services, such as Barracuda or Cloudmark. Typically these will blacklist a service provider for a short period of time, such as 12, 24 or 48 hours and then the blacklist is recycled and cleared. If they didn't do this then soon they would have every email provider on their blacklist and no email would get through.

If you need to get an email message to someone whose provider is blacklisting NCF mail in a hurry then you can:

  • See if you have an alternate address for the person to whom wish to send an email to and try that address instead
  • Use your own alternate email address to send your email to them, such as Gmail, Hotmail, or Yahoo

While most NCF members rely on NCF email, it is still handy to have an alternate email address to use. In normal circumstances you can just forward your Gmail, Hotmail or Yahoo mail to your NCF account and that keeps the alternate account available in case you ever need it.


If the blacklist doesn't clear in 24 hours or so and you still can't send a message to a certain e-mail provider the bounce back message may provide instructions for the NCF staff to help speed up clearing the blacklisting of NCF mail. Normally you can't do that yourself directly, though. You can see if there is already a posting about the specific issue on the NCF Help Desk Discussion Group and, if not, post one or send the information to NCF via an office message.

Some blacklists respond well to NCF system administrator requests for removal of NCF from a blacklist and others do not. Some blacklists do not take inputs at all and NCF has no means to make them take our mail, other than just waiting for the list to clear on its own.


The best way to prevent blacklist problems is to keep NCF mail off other provider's blacklists in the first place.

The easiest way to do this is for NCF members who run Microsoft Windows to ensure they use it safely as possible, including making sure that they are running an anti-virus application. Some recent surveys have shown that almost half of all Windows PCs are infected and are part of botnets. Windows users must keep their virus definitions up-to-date and run scans daily to prevent themselves from becoming part of spamming botnets.

If you are running Windows and do not have anti-virus installed some good free anti-virus applications are:

If you suspect your computer is being used for spamming (check your sent mail) then disconnect it from the internet until it is cleaned.

See also

Additional reading