IT Services Provider CRU Solutions Explains Why Spam Filters Don't Block All Junk Email

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Cleveland Managed IT Services provider CRU Solutions explains how spam filters work and how clever spam emails get through.

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Managed IT Services Provider CRU Solutions

There is no fool-proof way to eliminate ALL Junk Email short of locking filters down so strictly that it would block legitimate email.

According to [Cleveland Managed IT Services provider CRU Solutions, spam filters can block around 80% of the spam emails that come into a network, but cleverly-written spam emails can still get through.

It can be frustrating to see lots of messages in Junk Email, but it happens to everyone. There’s no 100% fool-proof way around it. Here’s why.

Most spam filtering software determines one of three things about every email that comes into a network:

  •     reject as spam and block from network;
  •     allow into Inbox;
  •     allow into Junk Email, tag the message, or quarantine it.

Messages rejected as spam include those that are sent to an invalid recipient address, from an invalid mail server, or fail to meet other criteria. These messages are blocked and no one in your organization will ever see them. This is around 80% of the email that enters a network.

Messages allowed into the Inbox include those that are sent to a legitimate recipient from a legitimate mail server and have passed through the multiple filters of the spam blocker as valid or are included in a white list.

Messages that appear in Junk Email are allowed because they have passed through several but not all of the multiple spam filters as defined by the needs of your company. The spam filter can’t determine the validity of the message, so it puts it in Junk Email for the user to decide.

Everyone has had the experience of finding a wanted message in Junk Email and wondering why. Without the option of Junk Email, that message would have been rejected as “close, but no cigar” by the spam filter and rejected, meaning the receiver would never have known the message was sent.

Clients sometimes ask us to “blacklist”, or permanently block, certain addresses from Junk Email messages.

If a message has made it to Junk Email, the spammer has designed the email cleverly enough to allow the main elements of the message to pass through the ‘definitely spam’ filters. Also, blocking one email address from one email won’t always stop more similar messages, because spammers change email addresses from email to email (to make it through filters).

The truth is, there is no fool-proof way to eliminate all Junk Email short of locking filters down so strictly that it would block legitimate email. Most spammers will send annoying messages for a little while, then move on.

Of course, the same basic rules apply to opening Junk Email that applies to all email messages:

  •     Don’t open a message from an unfamiliar source, just delete it.
  •     Never click on links or attachments in an email from an unfamiliar source.
  •     Financial institutions will not ask for your account number, Social Security Number, etc. in an email. If you’re uncertain, call your bank.

About CRU Solutions
Celebrating 30 years in business in 2012, IT provider CRU Solutions specializes in delivering Managed IT Services to small and medium-sized enterprises. Located in Cleveland, Ohio, CRU Solutions’ Managed IT Services include remote network monitoring and management, IT consulting, and IT support. Visit us at

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Janet Gehring
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