Hi Fai. You can actually email to tags in Evernote by utilizing the hashtag. For example, if you have a tag called Work you can email directly to it by appending #Work or #work to the end of the subject line. You can even send to multiple tags if you want. These things are not included in the post because it was written in 2009 and they are relatively new developments.
On a side note, if you were to use a system like this, utilizing Notebook Stacks (another relatively new feature), you could have one notebook with your contexts in several sub-notebooks, which you could then add tags to for drill-down purposes. Using the @ and # to email directly in would work well there.
Two caveats, however, when it comes to emailing directly to notebooks or tags:
1. Unless something is so obvious it hurts, it is actually faster and more effective in terms of GTD collections to simply send it directly to your inbox, and then tag it during the processing phase.
2. You have to be careful with naming tags and notebooks. Many people like to use the @ and # in tag/notebook names, and this can cause problems emailing directly to them.
Hope that was helpful! :D