I have created the Kanji a Day and Grammar a Day mailing lists because that's what I wanted to help study the
Japanese language myself. If they can help others study as well, then I am happy to make them freely available. As far as I know, these are only such lists on the Web.
There are actually 7 Kanji lists available, one for each group of Kanji that corresponds with the grade level in which they are taught in Japanese schools and one which covers all 1945 Joyo Kanji. And, there are 5 grammar lists, one for each JLPT level and one covering all four levels. You can sign up for as many or as few lists as you wish.
I must warn you that these list are in 'Beta' mode. Basically, that means I don't know what kind of weird
problems may appear or how reliable my mailing software will be. But, for the price (free) it should be worth it.
The emails are best viewed in HTML format; the text format emails are a simplified version intended for those who wish to use their mobile phones.
Encoding schemes for Japanese are a bit of a hassle - for the record, these emails are sent in Shift-JIS (SJIS).
The "free" email services (e.g. Hotmail, Yahoo!) are the most likely to have display problems. Especially, note that you must manually choose the Japanese encoding scheme when using Hotmail. Recently, Yahoo! mail and Google Gmail has looked pretty good though.