[4] Disguising e-mail addresses in a systematic manner (for example, user[at]domain[dot]com) offers little protection.
In contrast, well-maintained e-mail filtering on the user's end does not drive away potential correspondents.
No spam filter is 100% immune to false positives, however, and the same potential correspondent that would have been deterred by address munging may instead end up wasting time on long letters that will merely disappear into junk mail folders.
For commercial entities, maintaining contact forms on web pages rather than publicizing e-mail addresses may be one way to ensure that incoming messages are relatively spam-free yet do not get lost.
According to a 2003 study by the Center for Democracy and Technology, even the simplest "transparent name mangling" of e-mail addresses can be effective.