smtp.ehlo.no_smtputf8

SMTPUTF8 Not Advertised

What we check

We check the EHLO response for the SMTPUTF8 extension. SMTPUTF8 (RFC 6531) allows email addresses with non-ASCII characters — internationalized local parts like 用户@example.com and internationalized domain names in their native script — to be used directly in the SMTP envelope.

What this finding means

The server does not advertise the SMTPUTF8 extension in its EHLO response. Senders cannot deliver mail addressed to internationalized email addresses (EAI) on this server; such messages are rejected or bounced before transmission.

Why it matters

Internationalized email stays undeliverable. Users whose addresses contain non-ASCII characters cannot receive mail on this server. Adoption is regionally significant — several registries and large providers (including Gmail and Outlook.com) support EAI.
No workaround exists at the sender. Unlike 8BITMIME's 7-bit fallback, there is no downgrade path for a non-ASCII address: RFC 6531 requires the receiving server to advertise SMTPUTF8, otherwise the message cannot be sent at all.
Depends on 8BITMIME. SMTPUTF8 requires 8BITMIME; a server missing both is limited to traditional ASCII-only addressing.
No deliverability impact for ASCII mail. Regular ASCII-addressed messages are unaffected — this only concerns internationalized addresses.

How to fix

Support depends on the MTA:

For Postfix: available since 3.0 when built with ICU support — smtputf8_enable = yes is then the default. If it is missing on Postfix ≥ 3.0, check postconf smtputf8_enable and whether the package was built with ICU.
For Exim: requires a build with SUPPORT_I18N; smtputf8_advertise_hosts already defaults to *, so the build flag is the actual gate.
For other MTAs: consult the documentation for RFC 6531 / EAI support; some older or minimal implementations do not offer it.

How it's graded

Missing SMTPUTF8 is informational and carries no penalty. See Grading Methodology for the full scoring model.

Evidence example

C: EHLO scanner.example.net
S: 250-mail.example.com
S: 250-PIPELINING
S: 250-SIZE 52428800
S: 250-8BITMIME
S: 250 ENHANCEDSTATUSCODES
(SMTPUTF8 absent from capability list)

References

RFC 6531 — SMTP Extension for Internationalized Email