HELO identity
The host name a sending server gives in its SMTP HELO or EHLO greeting, which SPF can check against that name's own SPF record.
What it means
Every SMTP session opens with the client naming itself in HELO or EHLO. RFC 7208 recommends that receivers run SPF on that name as well as on the MAIL FROM domain, and check it first: a host name usually maps to one server, so its record is simple and a conclusive answer can save the more complex MAIL FROM check.
The HELO check only works when the name is a real multi-label domain, not an IP address literal. It also matters for bounces, which have an empty envelope sender: SPF then uses postmaster at the HELO name as the MAIL FROM identity.
A server's HELO name should be a real host name that resolves, with an SPF record of its own such as v=spf1 a -all. DMARC does not use HELO results.
Example
mail.example.com. TXT "v=spf1 a -all"Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 7208: Sender Policy Framework (SPF), section 2.3rfc-editor.org
- RFC 7208: Sender Policy Framework (SPF), section 2.4rfc-editor.org
All 432 terms in the glossaryThe wiki: blocklists and bounce codes