One option is to pay for mail hosting from a "big mail provider" or hosting company and simply use it only for relaying/sending outbound mail but not for incoming. Assuming 25/TCP inbound is not blocked by your ISP, you can point the MX RR at yourself and handle incoming mail on your own.
I work for an ISP and run my own personal mail system. This (25/TCP outbound being blocked/restricted) is, as you mention, one of the biggest hurdles for an average person to be able to run their own mail system (especially on their home connection). I've debated offering up a cheap "outbound relay only" service for fellow geeks but I would have to (initially, at least) institute some pretty low rate restrictions in order to help prevent any spam issues. That's the biggest thing stopping me from doing it so far.
one thing you'd lose that way is the direct secure delivery. not that it'd matter if you send it to someone on google, but you can't trust the relay server not to tamper with the mail
unlikely, but if you are the type to run your own mailbox, probably that matters to you
Good point, although if my options were either a) handle inbound myself, rely on a third-party for outbound or b) rely on a third-party for inbound and outbound, I'd pick the latter (although not everyone would, of course).
Obviously, you'd have to trust whomever you're using for relaying not to mess with your mail.
Another option could be a VPN connection to bypass ISP-level packets filters.
It would be a nice feature add-on if Own-Mailbox users could add a special TXT record to the DNS that identifies them as Own-Mailbox users. The presence of this record would tell Own-Mailbox that it could do a direct delivery to that user and get the increased end-to-end security. For all other outbound mail, it could use the provider's SMTP relay.
I work for an ISP and run my own personal mail system. This (25/TCP outbound being blocked/restricted) is, as you mention, one of the biggest hurdles for an average person to be able to run their own mail system (especially on their home connection). I've debated offering up a cheap "outbound relay only" service for fellow geeks but I would have to (initially, at least) institute some pretty low rate restrictions in order to help prevent any spam issues. That's the biggest thing stopping me from doing it so far.