Gregory's ServerEmail products I use:
1. Outlook.com
2. Microsoft 365 (work email)
3. Around 10 email forwarders associated with personal domains and products
4. Several IMAP/SMTP accounts on cPanel domains w/Roundcube web client
5. A couple of Tutanota accounts
6. A Protonmail account
7. Paid up Firefox Relay customer
8. DuckDuckGo Email Protection relay user
9. Mailbird email client on desktop
10. Several GMail accounts
Email is beautiful in its multi-faceted, interoperable glory.
cc @chriscoyier