smtp.ehlo.no_pipelining
PIPELINING Not Advertised
What we check
We check the EHLO response for the PIPELINING extension. PIPELINING allows a sending MTA to issue multiple SMTP commands without waiting for individual responses, reducing the number of network round-trips.
What this finding means
The server does not advertise the PIPELINING extension in its EHLO response. Without it, every SMTP command requires a separate round-trip — the sender must wait for a response before sending the next command.
Why it matters
- Performance. Without PIPELINING, a typical mail delivery requires 8–10 sequential round-trips. With PIPELINING, several commands can be batched, cutting latency significantly — especially over high-latency links.
- Widely supported. PIPELINING has been standard since RFC 2920 (2000). Not advertising it suggests an unusual or restrictive MTA configuration.
- No security impact. This is purely a performance concern with no effect on security or deliverability.
How to fix
Most MTAs advertise PIPELINING by default. If it is missing:
For Postfix: PIPELINING is built-in and always advertised. If missing, check whether a content filter or proxy in front of Postfix is stripping the extension.
For other MTAs: consult the documentation for your MTA to enable PIPELINING support.
How it's graded
Missing PIPELINING 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-SIZE 52428800
S: 250-8BITMIME
S: 250 ENHANCEDSTATUSCODES
(PIPELINING absent from capability list)