Outlook has it's Calendar that I use for tracking stuff, Thunderbird is my nod to when I need it across Windows, Linux, Android, and Apple.
What are others finding works best for email in Windows 7? I have to get a new computer and don't want W8 or W10, so it will be W7. But I am a HUGE fan of my XP Outlook Express. What have others found best? My email is filled with business correspondence, official documents, etc. and I MUST be able to transfer all the unsorted and sorted emails to the new computer without any kind of hitch!!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic