Can RClone give a transfer summary?

I use a cron job to copy new local content to a remote. Is there anyway to have rclone output only successfully transferred files in order to cut down on the size of the email I get from cron?

You could use grep as a way to find successful uploaded files and failed attempts using their pattern and using --stats and --verbose

Check out the documentation on Logging: rclone - Logging

If you use the -vv flag, rclone will produce Error, Notice, Info and Debug messages.