If you want the cheapest, no frills, secure (read their security policy) email host with calendar, contacts, tasks via caldav/cardav sync (thunderbird) then Purelymail is a great option. I have used them for years, no down times, great support, bring your own domain if you like. The only downside for some, it is based in the US. I am willing to overlook the US for a host that is $10 a year (can’t afford the others.)
If you worried about security, I would start thinking about transitioning off of Apple/MacOS and try out linux. Linux can run on your Apple computer. I assume you probably have an iPhone. I would suggest getting an Android phone (Pixels are great) and downloading an Android Privacy supported rom, like CalyxOS, which is de-googled completely, highly secure. There is also GrapheneOS and others, which support more phone manufacturers.
You are still exposed by using Apple products. Use linux for PC’s with encryption, vpn. For a phone, switch to device, such as a Google Pixel, or several other manufacturers that can use a privacy android rom. I use CalyxOS, private, secure and de-googled.
Lets not forget…operation PRISM which was exposed by Snowden.