Mysterious 403, 404, 406, 500 or "Page not found" errors depending on submitted content

When submitting certain words in content, you receive a 403, 404, 406, 500 or "Page not found" error message.

This behaviour is most likely caused by the Apache module mod_security. Depending on its filter settings, phrases that trip the module include

lynx, perl, mother, select from, table, cc:, and many more.

Ask your host to tone down the mod_security settings.

Alternatively you can try to add the following to .htaccess:

This will turn off filtering by mod_security.

Not all hosts will allow this, so you may need to contact your hosting provider.