Opened mail on my mac that I never opened

This may not be the right forum, but hopefully someone can shed some light on this mystery.

Yesterday I was sending an email from my mac mail desktop application and had to search for a file to attach. While I was looking in Finder, I noticed numerous files from my email account that were listed as being opened that day and the previous day. These files were very old emails and I hadn't looked at them in over a year.

Does anyone have any idea why my macbook would register a file being opened when I never had accessed it?

Thanks for any insight.