I think it would be a nice feature to have the composer validate the addresses and show some error dialog in case they aren't valid. I clicked on a mailto: link, which made me send an email to "user@domain.com*", that star at the end made the server reject my email, but I only got a very generic error from kmail and I couldn't understand what was going on. Luckily I had access to the logs of the server and could find the culprit in this way, but it would have been much easier if kmail had told me the problem. Reproducible: Always