I've been running my own mail services for close to 30 years now starting with handcrafted Sendmail configurations, now running Exim and Postfix. Running your own mail services isn't the scary problem it is made out to be.
There's the rub. 30 years ago this was true. Old systems have been grandfathered in.
A combination of rising spam and things like fraud via email have caused especially large services to be so much more aggressive in blocking. If your email has been around forever it's generally trusted.
The company I work for has been around for 15 years and we spent the first 5 or so getting yahoo and live/hotmail/outlook to accept our mail reliably despite proper dns/dkim/spf.
Self hosted on residential IP today is near impossible. Your only hope is pay to not be on a residential IP and even then strap in for years of struggle to get the biggest free providers to accept you as legitimate. Exacerbated by their thorough lack of actual support contacts.
This matches my experience from roughly 10 years ago. Even with a non-residential IP address, correct SPF, etc, it took months to navigate the biggest providers' obstacle courses for whitelisting. After succeeding with those, plenty of smaller providers remained to identify and work through one by one. And then, every so often, an already-completed one would revert.
It was not impossible, but even for someone experienced in email system internals, it was a slog that seemed never to be 100% done. I don't expect it's any easier today.
People tend to have all sorts of reservations against DeltaChat, even if they haven't tried it, and I just haven't experienced those problems.
I have tried DeltaChat with my own mailserver, and with Gmail, FastMail and DeltaChat's chatmail, and it has worked flawlessly. If it hadn't, I wouldn't be a fan.
This is obviously only anecdotal, so other people may report other experiences.
If used as chat only, and with dedicated chatmail servers, the number of theoretical problems diminishes significantly. Using it as an email client and/or with standard email providers introduces potential points of failure, but not more than email to email.
DeltaChat uses AutoCrypt to provide gpg/pgp encrypted “email” + metadata, and the chatmail servers are set up to refuse unencrypted messages (thus avoiding the spam problem).
The optimal experience is acheived by using DeltaChat the way it was intended: DeltaChat to DeltaChat communication, and I'd say that using the chatmail servers is also preferable to using custom IMAP/SMTP servers (whether they are hosted by the big providers, smaller providers, or self-hosted). You _can_ use DeltaChat to communicate to email-only recipients, but it provides for a sub-optimal experience.
It's cool that it uses email, but it's also not. Email is a notoriously painful standard to run a server for. I have ran a Matrix and Mastodon server, and I'm still running a BlueSky PDS, but I've never even tried to run an email server, since I know I'll get blocked the moment I try it for having a residential IP, and that it's a lot of work.
So most people will be stuck with commercial providers, with the largest happening to be Google, which needs users to set up an app password for DeltaChat to work. You've already lost most users at that point. Other large providers don't work or require setups: https://providers.delta.chat/
Then there's ChatMail relays, which are supposedly interoperable with email, but from the documentation it's very unclear to what extent that is. Not to mention that the possibility of them getting blacklisted by mainstream providers is very high, as they do text message analysis which doesn't work on encrypted blobs.
At this point, I have to ask: is email the right tool for the job? With all these drawbacks, it seems it would have been better to go with another standard, written from scratch.