What is the difference between

v=spf1 include:_spf.google.com ~all


v=spf1 include:spf.google.com ~all

(the first one is with underline character in front of the spf, the second one without)


spf.google.com doesn't exist, while _spf.google.com contains a valid SPF record.

In other words: only the first line will actually work (as of now).

If you search DNS for _spf.google.com you get the following result:

_spf.google.com IN TXT v=spf1 include:_netblocks.google.com include:_netblocks2.google.com include:_netblocks3.google.com ~all

Google is using the _underscore addresses to hold particular DNS records. There is no particular significance to the character choice; it's just their naming convention.


The "include" lets your spf record include another spf record, so it basically just points to a host entry.

The tool at http://www.kitterman.com/spf/validate.html also performs lookup on includes, and will tell you in cleartext that the host spf.google.com does not exist.

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