: Email 1.4 Lite supports integration with various third-party applications and services, enhancing its utility. Users can connect their accounts with calendar apps, task managers, and other productivity tools to streamline their workflow.

| Feature | Traditional Email | Email 1.4 Lite | |------------------------|--------------------------|-------------------------------------| | Header size | 1–5 KB typical | ≤512 bytes (mandatory: From, To, Date, Message-ID) | | MIME | Required for attachments | Disallowed (plain text only) | | Character set | UTF-8 | UTF-8 or ASCII (ASCII preferred) | | TLS | Opportunistic or forced | Optional (separate secure transport)| | Mailbox sync | IMAP IDLE/fetch | Entire mailbox dump + incremental patch | | Maximum message size | 25–50 MB typical | 8 KB (headers + body) | | SMTP extensions | Many (8BITMIME, PIPELINING, etc.) | None – bare-bones SMTP (RFC 5321) | | Delivery status | DSN (RFC 3464) | Simple boolean: 250 OK / 550 Fail |

The name "1.4" suggests a minor version increment from RFC 5322 (Internet Message Format, 2008) — not a major overhaul, but a disciplined subset.

Optional (but discouraged): Subject , In-Reply-To , References . No Cc , Bcc , Content-Type , MIME-Version .

: Comparison of constraints.