For you to maintain redundant connectivity, storage, and compute will immediately be a non-trivial workload. Then you need to keep it patched, and monitored, and backed up.

Then you have to run the mail infrastructure, possibly including a web front-end. postfix + dovecot + some-spam-thing. Blacklists. Spam signatures. DNS configuration, SPF, all the other hoops you need to jump through to get the big players to accept your mail.

After a lot of work, and mucking about, and ongoing expense and effort, you can end up with something that will probably be nearly-but-not-quite as good as what you'd get from a commercial provider.

BUT ... it'll be yours, and it'll be how the Internet was meant to be, and you'll be a part of the last bastion of open standards and cooperative distributed systems until such time as the big players decide that they're sick of SMTP and collude to produce a proprietary thing that looks like email, but kinda isn't, and you'll be left talking only to the other diehards.

Personally, I have taken a middle path: I use Pobox/Fastmail with my own domain. That way I maintain the control over it, but I've outsourced the work to someone who can amortize the costs over lots of accounts. I pay for the service, and have chosen a provider who doesn't try to leverage that relationship into a whole-of-life intrusion.