MyBB Community Forums

how to implement that all user must upload a attachment before post?

Hook into the post new thread and post new post hooks (I don't remember the exact hook names, they're in the Docs section) and just check if $post has an attachment. If not, don't post and throw error.

I've made a plugin for your needs.

You can only open a new thread if you upload at least one file with at least 1 byte of data on it.

Note: It only checks it at newthread hook, you can still edit the post and delete the attachment...