smtp.ehlo.no_size
SIZE Limit Not Advertised
What we check
We check the EHLO response for the SIZE extension. The SIZE extension tells sending servers the maximum message size the server will accept, allowing senders to avoid transmitting messages that will be rejected.
What this finding means
The server does not advertise the SIZE extension in its EHLO response. Without it, senders have no way to know the maximum message size before attempting delivery. They must transmit the entire message and wait for a rejection — potentially after transferring a large attachment.
Why it matters
- Wasted bandwidth. Without a declared size limit, a sender may transfer a 50 MB message only to have it rejected after the full transfer. The SIZE extension avoids this by allowing the sender to check before transmitting.
- Widely expected. The SIZE extension (RFC 1870, 1995) is standard in modern SMTP. Not advertising it is unusual and suggests a non-standard or minimal MTA configuration.
- No security impact. This is a protocol efficiency concern with no effect on security or deliverability.
How to fix
Most MTAs advertise SIZE by default. If it is missing:
For Postfix: SIZE is advertised automatically based on
message_size_limit. Verify the setting exists:# /etc/postfix/main.cf message_size_limit = 52428800 # 50 MBCheck for proxies. A content filter or SMTP proxy in front of the MTA may strip the SIZE extension from EHLO responses.
How it's graded
Missing SIZE advertisement 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: 250-8BITMIME
S: 250 ENHANCEDSTATUSCODES
(SIZE absent from capability list)