And I don't mean in a stalker-ish way...

How do you guys keep track of to whom you have written and when, what you chatted about, etc.?

I thought about scanning in the letters, but I'm not sure that's what will work for me.

Do any of you use spreadsheets, notebooks? If so how do you set it up? I recently started bullet journaling and I am trying to figure out a system for tracking my letter writing.