mail-not-arriving.txt
My <stack> app on <host> sends <what kind of email>. People say they
never arrive, or they land in spam.

Help me work out where they're going:
- Is mail leaving the server at all? How do I check on this host?
- Is the host blocking or rate-limiting outgoing mail?
- Are SPF, DKIM and DMARC set up for my domain? What should they say?
- Would a transactional email service be more reliable than sending from
  this host, and how would I switch?

Give me the checks in order, cheapest first.

Mail sent straight from a shared host's server often lands in spam, however good your code is. A sending service with the right DNS records usually fixes it outright.