smtp.ehlo.no_8bitmime
8BITMIME Not Advertised
What we check
We check the EHLO response for the 8BITMIME extension. 8BITMIME allows the transfer of messages containing 8-bit characters (non-ASCII content) without requiring the sender to encode them into 7-bit format first.
What this finding means
The server does not advertise the 8BITMIME extension in its EHLO response. Without it, senders must encode all non-ASCII content (international characters, binary attachments) using transfer encodings like base64 or quoted-printable before transmission.
Why it matters
- Encoding overhead. Without 8BITMIME, all non-ASCII content must be encoded, increasing message size (base64 adds ~33% overhead) and processing complexity.
- Universal support. 8BITMIME (RFC 6152, 2011) is supported by virtually all modern MTAs. Not advertising it is unusual and may indicate a very old or minimal SMTP implementation.
- SMTPUTF8 dependency. The SMTPUTF8 extension (internationalized email addresses) requires 8BITMIME. Without it, internationalized email features are unavailable.
- No deliverability impact. Senders will simply use 7-bit encoding as a fallback — messages still get delivered.
How to fix
Most MTAs advertise 8BITMIME by default. If it is missing:
For Postfix: 8BITMIME is always advertised by default. If missing, check for a proxy or content filter that strips EHLO extensions.
For other MTAs: consult the documentation to enable 8-bit MIME support.
How it's graded
Missing 8BITMIME 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 ENHANCEDSTATUSCODES
(8BITMIME absent from capability list)