1. Personal domain, currently hosted with Office 365 but I will probably move after the year is up.
2. Student email (.edu, G Suite). Used for all school business, school-related apps, and some things I haven't bothered to move to #1 yet.
3. Gmail account for spammy/annoying websites and signups.
4. Gmail account used for public records/FOIA requests, nothing else.
5. iCloud account (basically used for nothing except iTunes receipts).
6. ProtonMail account--used for my VPN accounts only.
On my Mac mini and iPhone, I use Apple Mail with 1, 2, and 5 added. On my Windows laptop, I access 1 and 2 through webmail (I have Outlook installed for 1 but rarely use it). Anything else, I just sign in to webmail as needed. I also have access to a few team/shared Gmail/G Suite accounts, I don't have these added to Mail b/c I don't want their unread statuses messing up my unread badges.
Only 1/2 are generally used for IRL stuff or accounts that I care about. I follow inbox zero and turn off email notifications for all but the most important stuff (ex security alerts, receipts, eBay auction results) and email analogs (ex. Canvas messages).