I haven’t used SimpleLogin. In Fastmail you can create aliases, which in Fastmail are email addresses you choose, and masked email addresses, which are generated with two random words and 4 random numbers under a domain of your choosing (any domain you own and have configured in your Fastamil account or a selection of Fastmail-owned domains). You can create masked emails quite easily (there’s a button in the inbox menu). Aliases have to be created through the account settings, so it needs mocre clicks, but it’s still quite easy. You can also set up a wildcard address for a domain you own.
You can reply from both aliases and masked addresses. When composing an email, there’s a drop-down in the from section that allows you to choose one of your aliases or masked email addresses and also the wildcards you might have set up. If you choose one of the wildcards, you can type any email address for that domain, even if it’s not any alias or masked address you might have.
I don’t know about Outlook, but it does have IMAP and I believe it also has active sync.
It’s possible to share email folders with team/family members.
You can invite and get invited to calendar events through the standard, so it’s cross compatible with other calendar services like Google’s. You can also Share a whole calendar with another team/family member.
You can assign different licenses to each user in your team/family and get charged accordingly.