In Lotus Notes 8.5, is there a way I can automatically search received emails for a certain string and add a hyperlink/hotspot to every occurence of this string?
For example, can I make it so every email I receive containing the string 'Stack overflow' hyperlinks that text to stackoverflow.com?
Yes, there is a feature in the Notes client called "Live Text" that allows you to set up text patterns and actions and wire them together to do what you want. Here is a link to an article that describes the feature.