Everyone seemed like they were interested in the way I log my mail, so I decided to write up a short post about it. Though the biggest piece of advice is: do what works for you!
I start with a journal. This one has a hard cover with a pen sleeve on the side (SO HANDY!). If you are interested this journal is actually a Reflexions sketchbook and is similar to a moleskine with heavier weight paper. (It was a gift, but I am thinking I may invest in more like this one.
Again, I don't expect this to work for everyone, but it works for me. I have tried multiple ways to make a mail log, even used a database for a while...but I couldn't get into the habit of marking it down. Somehow computers and letter writing do not mix so well.
You can also read about how the Missive Maven keeps her mail by clicking her name.