Spam Email: Can I block an entire Domain?

Dennis Faas's picture

Infopackets Reader Michael E. writes:

" Dear Dennis,

I read your newsletter all the time; thanks for publishing. Question: is there a way to block an entire web domain from sending email to me? I use Microsoft Outlook. The reason I ask this is because I constantly receive spam email from numerous web domains which seem to exist for the purpose of sending spam emails only, and therefore deserve to be totally blocked. I would like to be able to fill in a domain name in Outlook, and then never see emails again from those web domains in my inbox. "

My response:

Unfortunately, blocking an entire email domain is not an effective way to block spam because the FROM: field in an email can be forged. Most likely the domains you are receiving emails from don't even exist. Even if you blocked an offending domain, spammers will make up another randomly generated domain name, and spam will make its way straight into your inbox.

A better solution for blocking spam would be to choose an email service provider that incorporates numerous anti-spam technologies. For example, SPF (Sender Policy Framework), DKIM (Domain Keys), greylisting, DNSBLs / RBL (DNS-based Blackhole Lists) all operate at the mail server level and are very effective at blocking spam.

Yahoo, AOL, Hotmail, GMail, and all the other major email service providers already use these technologies, and because they operate on the mail server, there is need to configure your email client to use them. Unfortunately they are not 100% effective, which is why some spam email will get through and some legitimate emails will be redirected to a spam folder.

Using Email Filters to Pre-Screen Emails on the Mail Server

In conjunction with a reliable email service provider, another layer of protection would be to use email filters to pre-screen your messages before they download to your inbox. Mailwasher is a program that can do just that. Offending messages will be marked for deletion automatically; simply press the 'Process' button to delete, then use your email client to download the messages to Outlook for archiving.

An example email filter might be: "If an email message body contains an http link, mark it to be deleted". Most spam mail contains http links and most legitimate email does not, so this would be a very effective filter. If you have friends that send you a lot of http links, you can override the filter with a 'friends list'. You would then have to keep a careful eye on your emails for the next few days to ensure legit ones aren't being marked for deletion, but this would be very effective at catching most unwanted junk mail.

If you need help setting up email filters using Mailwasher or another email program, feel free to contact me and we'll set up a time to meet using remote desktop support.

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I need more computer questions. If you have a computer question -- or even a computer problem that needs fixing -- please email me with your question so that I can write more articles like this one. I can't promise I'll respond to all the messages I receive (depending on the volume), but I'll do my best.

About the author: Dennis Faas is the owner and operator of With over 30 years of computing experience, Dennis' areas of expertise are a broad range and include PC hardware, Microsoft Windows, Linux, network administration, and virtualization. Dennis holds a Bachelors degree in Computer Science (1999) and has authored 6 books on the topics of MS Windows and PC Security. If you like the advice you received on this page, please up-vote / Like this page and share it with friends. For technical support inquiries, Dennis can be reached via Live chat online this site using the Zopim Chat service (currently located at the bottom left of the screen); optionally, you can contact Dennis through the website contact form.

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