This reminds me of that "hackproof" box BBC reviewed that was a Raspberry Pi that couldn't update itself.

Also, having run an email startup in London, patching and anti-spam at almost any scale is nontrivial.

For personal mailboxes we're running exim on a managed VPS with a dedicated IP at a small hosting company. They have very diligent customer support and appear to keep their IP allocation clean, as we've never had problems with our emails being filtered as flagged as spam. They generally handle patching and configuration when we ask them to, or assist us when we want to do it ourselves.

For volume mailing we use ESPs like Mailgun and Sendgrid. Occasional deliverability problems are a fact of life at those.