Do SPF Records For Primary Domain apply to subdomains?

Question

I have a quick question regarding SPF records: Do they need to be present for all subdomains?

Lets say that I have a TXT record with SPF info for domain.com

Let's also say that I have a seperate email domain for subdomain.domain.com

Will the SPF policy/info for domain.com also apply to the subdomain? Or do I need to add a separate TXT record for that too?

Answer 1

You need to have separate SPF records for each subdomain you wish to send mail from. http://www.openspf.org/FAQ/The_demon_question

This makes sense - a subdomain may very well be in a different geographical location which will have a very different SPF definition.

EDIT - the 'include:' directive for SPF may be used to provide all subdomains with the same entries. For example, on the SPF record for subdomain mailfrom.example.com enter 'include:example.com'. In this fashion whenever you update the definition for example.com your subdomains will automatically pick up the updated values.

Answer 2

No, but you can short-circuit them with the include:maindomain.invalid directive.

Answer 3

In addition to the other answers, if a subdomain is created as a CNAME record, the SPF record is the one for the domain it points to, e.g. sub.domain.com is a CNAME of otherdomain.com, the SPF a mailserver will get when it looks up mail@sub.domain.com is in the DNS record for otherdomain.com. This is the same in practice if the CNAME record says sub.domain.com => othersub.domain.com, so your TXT record would need to be othersub, not sub. This is in contrast to DKIM, which needs a separate TXT record for the public key, even if your subdomain is a CNAME.