https://www.techradar.com/news/skypes-new-read-receipts-let-you-know-that-your-message-was-received

It looks like a major change is coming to the Skype app, with Microsoft introducing read receipts to the preview version of the software.

You’ll likely be familiar with read receipts from using other messaging platforms. Essentially, what happens is that the sender will be notified when the person who receives their message has read it. So, even if there’s no response (at least initially), you know that the message has got through.