Earlier quoted context omitted.
If you have enough experience or make enough simplifying assumptions, anything is trivially easy. But it doesn't take much imagination or experience to see that bootstrapping your own email isn't trivial. For instance, I defy you to buy a domain name and a hosted debian machine without maintaining an existing email account. As a developer / sysadmin who used to host his own mail and uses complicated half insane APIs…
(1) use public email account to buy domain + hosted debian box (2) set up mail server, create account(s) (3) reset public email account with domain registrar + hosting facility to newly set-up email addresses (4) kill public email account You only need one for a very short while to bootstrap your own email server, you don't need it forever.
But I'll bite, if your mail server goes down - and it will - you now have no email. You can't email your hosting support. You try to log in to your host control panel to do a reboot or raise a ticket but forgot your password. You can't get the reset email. Somehow you manage to login and raise a ticket but won't get any email notifications when the technician responds asking for your server id number...