SMTPUTF8
An SMTP extension (RFC 6531) that allows UTF-8 in email addresses and header fields, needed for addresses written in non-Latin scripts or with accented local parts.
What it means
A server that announces SMTPUTF8 accepts the SMTPUTF8 parameter on MAIL FROM and, with it, addresses whose local part or domain contains non-ASCII characters, along with UTF-8 header fields as defined in RFC 6532. Servers offering it must also support 8BITMIME.
Every hop has to support it. When a message needs SMTPUTF8 and the next server does not offer it, the message cannot go further as it is and bounces; the enhanced status codes 5.6.7 to 5.6.9 describe such failures. A non-ASCII domain can fall back to its ASCII (punycode) form, but a non-ASCII local part has no ASCII equivalent.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 6531: SMTP Extension for Internationalized Emailrfc-editor.org
- RFC 6532: Internationalized Email Headersrfc-editor.org
- IANA, SMTP Enhanced Status Codes registryiana.org
All 432 terms in the glossaryThe wiki: blocklists and bounce codes