I recently got Stalwart running with Bulwark as the front end to actually send emails. I have Stalwart behind Caddy for https and Stalwart only exposes http because I don't want to mess with pop and imap. Instead I have it using JMAP, which Bulwark is designed for, because it's simpler and more secure. Receiving emails works from some basic testing against my personal Gmail account. Sending email was a bit more complicated, but I ended up using SMTP2GO for outgoing mail and it worked in aforementioned testing. Their free tier is more than enough for personal email and I can switch to a different smtp relay in the future if I choose to.