I described about 10 posts ago the differences I discovered comparing the
legacy Enhanced with the current
Standard plans.
I upgraded my
Enhanced account to
Standard earlier this year. I also have a
Basic account. Let me know if I can answer any questions you can't discover with my earlier post or these help pages:
https://www.fastmail.com/pricing/
https://www.fastmail.com/help/account/limits.html
You can of course file a normal Fastmail support request with any specific questions.
Bill