Email Spam, Blacklists And Whitelists Explained

What is Spam?

spam-iconEmail spam,,junk mail or Unsolicited Email is email you receive that you don’t want, or didn’t ask for, and is sent by someone you don’t even know.

In the early days of email spam was a big problem.

Although spam hasn’t disappeared, it is now usually taken care of on the email providers servers.

Most email providers,including free providers like Gmail provide some form of spam detection and blocking.

How Spam is Detected?

Anti Spam Software works by analysing the content and sending address of emails and flagging suspect email as spam.

In general there are three mechanisms that can be used by spam filters or spam blockers. They are:

  • Word filtering
  • Blacklist filtering
  • White list filtering

Word Filters

This is the most common mechanism used.

Spam filters examine each message looking for “spam-markers” such as common spam subjects, known spammer addresses, known mail forwarding machines, or simply common spam phrases and keywords.

If any of these conditions are met, the message is classified as spam (junk mail).


A black list is list of email addresses from known or suspected email addresses that are sending spam.

Email from an address on a blacklist is immediately marked as spam.

Anti spam software can use exiting Backlists, and create their own blacklists from emails that they flag as spam.

Because spam filtering software is not 100% accurate innocent emails can be flagged as spam.See False positives


These are the opposite of blacklists and tell the spam filtering software to ignore email from white listed email addresses as the email addresses are trusted,

Sever Based BlackLists and Whitelists

Free Email providers like Gmail,Yahoo Mail provide some degree of spam filtering,  and use Whitelists and Blacklists usually provided by commercial provider like Spamhaus.See Spamhaus block list.

If you use email lists for email marketing purposes then you need to be aware of these lists.

Gmail places email that it has detected as spam in the spam folder. This support article explains how Google spam detection works.

Yahoo also place suspect email in the spam folder. This support article explains Yahoo spam policies.

Personal Blacklists and Whitelists

Email clients like Windows Live Mail and email services like Gmail and Yahoo Mail may also allow you to configure you own personal blacklists and Whitelists.

Creating Your Own Blacklists

On Yahoo Mail they are called blocked addresses and you can add individual email addresses or domains to the blocked senders list.

Go to Settings>Blocked Addresses and add the addresses.

On Windows Live mail go to Options>safety>options and add the addresses to the blocked senders.

On Gmail go to Gear icon>Settings>filters and blocked senders to view the blocked addresses.

To block an address you need to open the email and select more options to block it.

Creating Your Own Whitelists

Not all email systems support white lists e.g. Yahoo Mail doesn’t.

On Windows Live mail they are part of the Safety Options. Go to Safety Options and select Safe Senders and add the addresses to the list.

On Gmail you need to create a filter. Go to Gear icon>Settings>filters and blocked senders to configure a filter.

False Positives-The flip side of fighting Spam

A False Positive is a legitimate e-mail that is incorrectly blocked by a spam filter because it identifies it as spam.

While accidentally deleting email from a friend may be inconvenient, the loss of an email from a customer, client or prospect could be costly.

When setting up and configuring anti spam measures and software be aware of the necessity of not blocking legitimate email.

There is no point in choosing an anti spam solution that is 100% effective against spam but also blocks 70% of the legitimate email.

Common Questions and Answers

Q- Does Windows live mail place messages in the same spam folder as Gmail and Yahoo Mail.

A- No it uses the Junk email folder.

Q- Should I check my spam and or Junk email folder periodically?

A- Yes. You will often find that messages are marked as spam when they aren’t. Drag them back to your inbox.


Spam filtering and detection can take place on the email server and on the email client.

If you are using a desktop based client like Windows live mail with Yahoo Mail, Gmail etc then you will almost certainly have two levels of spam detection.


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