1. Use a contact form. Don't make your email address public. Especially not as a clickable link. Here are some more reasons to avoid using clickable email address links.
2. Use a different email for each site you sign up for. Then if one email account starts getting spammed, you only have to change it in one place. This is more to do with email spam than blog spam, though.
3. Use a different email when posting comments. Who knows if the blog you're commenting on will keep that email private? They might start sending you messages you didn't ask for with no way to unsubscribe. Best to use a dedicated email address just for posting comments.
4. Banning IP addresses. This is a bit extreme unless you notice some very clear patterns in the spam you receive. Also, be careful, as banning by IP can also block legitimate Internet use.
5. Moderation. This means that every comment on your blog will be held until you approve it. The downside is that it requires a lot of manual effort, and may not be an option for blogs that get hundreds of comments every day. However, if you can add users to an "approved" list so you only have to approve their first comment, this seems like a very sensible solution to the spam problem. Well, unless your blog attracts lots of new users every day and many of them only write a small number of comments.
6. Anti-spam plugins. WordPress users will probably know about Akismet, a plugin that analyses comments as they come in and attempts to flag the ones that look like spam. Generally, it works well, but no system is perfect - the most common issue I've seen is the problem of false positives (i.e. legitimate comments being flagged as spam). So you do need to check that the right comments are being let through and that the bad ones are being flagged.
7. Word verification. Also know as a CAPTCHA, this uses an image of distorted letters and numbers and requires you to type the characters into a box. Get it wrong and you have to try again. I think these are quite effective so long as they are easy to read - I've seen some CAPTCHA images that are really terrible! However, a few people have problems with it, either because they can't read the text or because the system tells them they mis-typed the text when they didn't (I've seen examples where it doesn't work for reasons unknown). Finally, there are some people who refuse to comment on sites that use word verification.
8. Closing comments after a specified period of time. This method works on the assumption that a few months down the line, nobody will want to add anything new to your post. Spammers seem to enjoy targeting posts that have long since disappeared from the front page of a site, hoping that the site owner won't notice the spam. I've had some great comments weeks or even months after I originally published a blog entry, so at first glance this method doesn't seem logical to me.
However, I recently learned a little more about this when I wiped benbarden.com and started again, deleting all the old posts. Suddenly my comment spam stopped. I did notice some weird things happening and discovered a bug that allowed people to comment on posts that didn't exist - so they weren't even using the conventional way of commenting, it was obviously someone with a script to automatically submit comments to my blog. Once I plugged that hole, the spam stopped.
It's not a permanent fix - and I understand that most sites would never delete all their content! Once your new posts get picked up by search engines, there's a chance for the spam to creep back in, But if you close comments after a certain amount of time, this can really cut back on your comment spam.
9. Requiring registration. This is likely to limit your comments drastically, and is still not a guaranteed way to stop spam. It's a good method for blogging networks or sites that offer more than just a blog, but it's a bit too draconian for most blogs.
10. Turning off comments altogether. No comments, no spam, right?! OK, you might not get any comment spam this way, but don't cut off your readers! This method is a bit extreme - does anyone use it?
Which methods do you use? How effective are they?
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