Topic: standards
-
vCard 4.0 basics: the text/vcard format for exchanging contacts
A vCard is a UTF-8 text/vcard document of BEGIN:VCARD, VERSION:4.0, a mandatory FN and optional structured properties (N, TEL, EMAIL, ADR, UID, REV) with parameters; values escape commas, semicolons and backslashes, and content lines fold at a maximum of 75 octets. jCard (RFC 7095) carries the same model in JSON.
-
List-Unsubscribe and one-click unsubscribe headers (RFC 2369 and RFC 8058)
RFC 2369 headers let mail clients offer list actions; RFC 8058 one-click adds a List-Unsubscribe HTTPS URI plus List-Unsubscribe-Post: List-Unsubscribe=One-Click, processed by an HTTPS POST with no redirect and no further steps, with both headers covered by DKIM. Bulk senders are required by Google's guidelines to support it.
-
Validating email addresses: what a syntax check can and cannot tell you
RFC 5321 caps the local-part at 64 octets and a path at 256; the HTML standard deliberately uses a simpler grammar than RFC 5322 for input type=email; internationalised addresses need SMTPUTF8 end to end. Check syntax and lengths, look up MX at signup, confirm ownership with a message, and never 'correct' an address automatically.
Machine-readable: JSON