I'm myself using a non-profit email redirection service as my main e-mail address. They do not provide an email box, just the redirect, so they can keep the service lean with a very modest one-time fee for new members.
This allows me to change the actual e-mail provider when needed. I already moved (successfully) away from Gmail, and I'm currently considering moving again as the spam protection of my current paid-for email service isn't that great.
I think the redirection service is ingenious. Sadly it isn't available worldwide, so I won't advertise it here, but I'm sure there are others like that.
Sent via the email provider, but I'm using clients that can set a custom "From" and/or "Reply-To" header fields, containing of course the redirecting address.
To be frank I haven't even thought to consider DKIM, so I guess it's fair to say it hasn't been a problem. This is a private e-mail address with quite low number of outgoing e-mails, so hard to say how universal my experience on this is.
I have a DigitalOcean droplet running Postfix, which provides edge security and a private IP, but no storage. All my mail is routed through this droplet across a VPN to my home Exchange server. Exchange backups are encrypted and stored on Amazon Cloud Drive. Yes, there's a reliance on cloud services for backup storage, but the only time I'd need the offsite backup is if my home servers both became unavailable for some reason. I'm happy with taking the chance that, if that happens, it won't happen at the same time as Amazon closing my Cloud Drive account.
I admit though, this is probably over the top for most people. I do it because email is my job, so it's useful to have my own servers for testing stuff.
The parent poster is correct and it's a good assertion. I'm doing the same thing, even though I'm using Windows as a base operating system, primarily for convenience at this point in time.
Email is very portable if you keep it in a place you control. You're pretty much just paying for a collection and caching service if you use POP3/IMAP and store your important folders locally. That is portable in a couple of hours between hundreds or thousands of different companies who operate standard protocols.
And then there's the possibility of running your own MX with postfix/dovecot etc if you really want.
