Is there a way to capture the opening of an email sent as an activty of the opportunity object for example? I wrote a trigger on EmailMessagge (after update) but is not invoked.
There is not currently a way to capture this. The updating of
EmailMessage.Status from 0 (New) to 1 (Read) that occurs when a user opens the message does not fire triggers. You can vote to change this on the IdeaExchange.