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Your ISP and Spam Filters

Unlike the Post office, your ISP is under no obligation to actually deliver your email to you. They can deliver  whatever they want, block whatever they want, and send whatever they want to a spam folder. Understand these three conditions.

  • They deliver your email.
  • They decide the email is spam and put it in a special spam folder, possibly on their server forcing you to go there to check it.
  • They refuse to accept the email at all, so you never even know it was sent.When they refuse an email, it is returned to the sender.


ISPs blocking email

Some ISP's subscribe to many lists of "known spammers" and simply block and discard any email from any address on any of those lists. Most of those list owners are legitimate and conscientious and work hard to maintain an excellent list. Other's have lousy lists and provide no way to remove yourself if somehow you were incorrectly put on such a list. My IP address was put on one such list and they will not communicate with me at all. They will not tell me why my name is on the list or what can be done to remove it. Canby.com subscribes to that list along with many other lists, so I frequently have trouble sending mail to any of my clients in Canby. Sadly, there is often nothing that can be done if they discard emails from your vendors or clients who were put on any of 30 or 40 lists maintained by someone who refuses to respond to false listings. I have never found an ISP who would stop subscribing to a list simply because it was incompetently maintained and provided no way to remove a name falsely added.

Usually it is possible for you to whitelist an address so that will override the email blocking. If this is happening to one of your clients or vendors, try and work with your ISP to whitelist that sender and to help that sender get his name off the list. More than once I've  had one of Comcast's servers get on  a list, because someone using that server was reported as a spammer. Comcast can normally get their server removed pretty quickly, but smaller businesses often have much more trouble.


Email Spam Filtering

Unfortunately there is no perfect way to be sure an email is spam. Really good spam filters catch nearly all your spam and very rarely think good email is spam. For a long time I recommended that my clients simply disable their ISP's spam filtering because some ISP's are incompetent. I recommended that my clients handle their own spam filtering.

If you decide to handle your own spam filtering, then see if Thunderbird's built in spam filtering is good enough. If not, Mailwasher Pro is a good investment. You can buy it at http://www.firetrust.com⁄  The free version might be all you need, you can check it out here: http://www.mailwasher.net⁄.

Because I don't trust Comcast, I have my Comcast email forwarded to Gmail and use Gmail's spam filtering to pre-sort suspected spam for me. It catches 95% of my spam and only rarely puts good mail into a spam folder. To my knowledge, it has never simply blocked and discarded mail sent to me. I wrote an article about how to use Gmail to filter your spam here.


Competent ISPs

Most ISPs are now reasonably competent and their spam filtering works pretty well. However, to work with them, you must check your spam folder frequently. I find that if there are more than 20 or 25 spam emails in the box to be checked, then I don't spot the good ones very well. I am likely to miss an important email from a client or vendor. For this reason I suggest checking the spam box every day, or maybe twice a day.



Either control your own spam, or make sure you are reviewing your filtered spam daily for false positives. The easiest way to check your ISP's site for spam, is to setup 2 Home pages. This way, when you open your browser, you'll get your normal home page and also your Webmail page. I wrote an article about setting up multiple home pages last month.


Date: July 2008

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