As @silisili noted, maybe Evolution could work for you. If you have a spare machine, maybe give one of the more boring Linux distributions a try and install Evolution, and test out your workflow with it. Don't try to customize things beyond what you need for your workflow. Just tweak it enough to fullfill what you need to do your job. Plus try out the printing via your Dymo printer...and see how it goes. If there were other apps, i wouild suggest trying them out via WINE...but maybe that's not needede for email and Dymo printer? Good luck!