Exim and Dovecot. With a clean IP on a VPS and SPF, DKIM and DMARC I haven’t really encountered any problems yet. Though I’m only doing it for about 2 years.
This is the way. Exim is far easier to config than Postfix, which is what I’m using now. I’d run Exim before for years, but thought I’d try Postfix since it’s the popular kid. It was a mistake, but everything is running and stable, and… well, sunk costs is keeping me from reconfiguring my set-up.
It’s a bit of effort to get everything configured correctly in any case, because of the number of moving parts. SPF and DMARC on the DNS entries, dovecot, Postfix or Exim, and a spam manager. Spam management consumes a huge amount of resources.