According to this page https://harmon.ie/documentation/sharepoint/outlook/savingemail users should be able to see if an email has been archived by a colleague and co-recipient.
Snip from the documentation: "If your email recipients reside in the same domain, the Saved Location button appears for them when they view an email message you saved to SharePoint. Contact your administrator if this option is not available to you. "
How do I activate this feature if it is not available?