I have tried Fastmail in the past for personal usage and was happy with it. I wish I'd have stayed with them for that particular use case, but alas.
Happy to have a chat and explain my use case. Don't have the time now to do an in-depth comparison.
Have a look here : https://www.fastmail.com/help/receive/stopspam.html
Fastmail have CardDav + CalDav endpoints but android still not support these protocols.
I'm using Fastmail everyday and I advice you that if you are an android everyday user, to go to Gmail.
Basically, ensure everyone realises that their google 'account', even though it seems to include everything, isn't theirs and is never changeable to a personal one.
I have one, purely for using a custom domain from a few years back, and now find that my 'Google everything' account is completely useless for some things and I have to create a brand new personal account - everything in the play store, or wallet or anything else is wasted.
I'd go with Fastmail and keep it outside of the Google 'everything'.