How do I disable threading/conversation view, so I see each message by itself?
Unfortunately, Mailspring only supports Gmail-style “threaded” message display. When new replies arrive to existing messages, they’re disabled as a single grouped “thread” in the relevant folders / Gmail labels.
This is largely for historical reasons—Mailspring is the successor of Nylas Mail, which used the Nylas APIs and closely mirrored Gmail’s APIs for email actions, meaning there was no way to perform an action (eg “move to folder”) on a single message, only on a full conversation.
However, because of some changes we implemented in Mailspring since, it should be possible to do this. Most users prefer conversation-style threading, but if you would like to see threading made optional, upvote this feature: Make Threading/Conversation View Optional