Elm creator Evan Czaplicki describes implementing SMTP delivery and domain authentication but seeing different outcomes at Gmail and Outlook. He argues that managing domain, IP and network-block reputation is harder than writing the sender. His account of Outlook’s block-level filtering is speculation, not verified knowledge of its internals. Microsoft’s documentation likewise describes SPF, DKIM and DMARC as parts of a broader protection system. Self-hosting decisions should distinguish successful transmission from actual delivery and include monitoring and reputation-management costs.