Another reason why I will always like Domino and Notes more than …

… other mail clients, because of the things I could do with it.
Once I translated the OpenNTF mail client to German and I added some features, like views with different categories. Sent and received for the same email address for example. I liked that much better than having to sort things manually into folders. Unfortunately, they broke with the Java views. I never figured out how to make them work with more than one categorisation.
I hate folders, but the big advantage of the Notes folders are, documents can reside in different folders. I had a function for my mailbox that added the same mail to different folders and left it in the inbox.
Or the integration of mails into Notes based CRM systems via embedded views. I used that on several CRM systems I either worked on or developed from scratch. Some people didn’t even use their mailbox anymore.
With what other mail client can you do that?