Out of sight, out of mind
All my life, I’ve had a “junk drawer” for those odds and ends that didn’t really go anywhere else or I didn’t want to deal with right then. Since I didn’t have to look at them, the contents usually got ignored for a good long time before I’d sort trash from treasure. Now I’ve also got a junk email folder. While the contents of the folder and the drawer are quite a bit different, every so often I still need to go through that folder and see if there’s any treasure among all that trash.
As tempting as it is to leave your junk email folder as “out of sight, out of mind”, it is actually something you should look at occasionally to make sure nothing that you actually want ends up there. Thunderbird, along with almost every other email program, has the ability to “learn” what you consider to be junk mail. This is usually a really good thing since, after a bit of training, the amount of junk mail you see goes down. But junk mail filters occasionally make mistakes and, if you don’t correct these mistakes, they “learn” the wrong things.
The recommendation for email with any sort of “learning” junk filter is to check the junk folder often when you first start using it. And if you’re expecting an email that’s not shown up or if someone says they sent you an email and you’ve not seen it, it’s a good idea to check the junk folder. As time goes on, you junk filter “learns” about your email and you should see fewer mislabeled genuine email messages so you can check the junk folder less frequently. As far as how often you should go through and clean out the folder, a lot depends on how much junk mail you get and how much time you can stand to spend going through the junk. I’d recommend at least once a month since some email programs delete anything marked junk that’s older than a month.