When a message is moved between folders, instead of updating the folder information, it is actually deleted from the original folder and created in the new folder. This is the standard process. When the message is deleted but not yet created in the new folder, you can receive a 404 error for GET API calls. Usually, this is seamless except for some IMAP providers with poor performance where sync is usually slow.
If the message is moved on the provider and the provider shows poor performance or sync delays, you can expect to see 404 errors for a while until we can sync the message in the new folder.
If the message is moved via PUT API call you'll see a new parameter in your GET API call
message_state = soft delete. This is a flag that means that the message is waiting to be created in the new folder while it has already been deleted from the original folder. So it is in a
soft delete state. When the message is in the
soft delete state, its folder property is null.
Messages in this sync state should be treated differently than the regular messages since they are still processing.