SMTP 250 is not delivery: three receipts that fix transactional mail

Sun, 11 Oct 2026 08:00:00 -0600

SMTP returns “accepted” for a message the relay may still lose ten minutes later, and APPEND is not delivery. After this, an engineer auditing a transactional mail system can name the three receipts (machine-written records proving each step really ran) that recover the truth, explain why each is non-negotiable, and check their own system against them.

The receipts come from a recent design pass on Catalyst’s correspondence subsystem, but the problem belongs to any system that sends mail through a hostile network. SMTP is honest about the protocol. It is silent about what happens after.

Smtp on Start AI Tools - Presented by Intent Solutions

SMTP 250 is not delivery: three receipts that fix transactional mail