This issue looks like it has been resolved for JIRA but I'm having the same complaints from my users in Confluence. I'm not sure it's been fixed, but wondered if there was a work around or if others having same issue?
"I just noticed today that if you attach multiple files using the Drag and Drop Attachments plugin it sends a separate notification per file even though i highlighted all the files and dragged them all at the same time. This is flooding the users inboxes with useless notifications and causing them to disregard email notifications even more than usual.
Is there a way to tone this down? Or can this be resolved in a newer release so that we only get 1 notification for a single drag and drop?" https://answers.atlassian.com/questions/136540
https://ecosystem.atlassian.net/browse/JDDAP-39.