You can read and possibly even search mailing list archives OK, but if you want to ask a question or answer a question, you have to sign up for the list. Then you get all these emails from the list which are a pain. OK, you set up a filter and put them all in a nice little sub-folder, which you forget about until your mailbox is full. And it's a pain to search that sub-folder. And it's not easy to browse through the emails to find the ones you're interested in, like it's easy to browse around on a forum. And the data is organised chronologically rather than by topic (if you have a mail client that can sort by threads, it's a little better). And people reply on or off list in an unpredictable way, so you don't know if someone before you who asked the same question actually got an answer. And you can't link to messages in your own mailbox. (You can link to the contents of a mail archive, but that's a whole extra separate step.)