HI there - i've searched through this forum and a ton of others but wanted to check some specifics of my situation. any help gratefully received and sorry if this is obvious:

i've setup linode to host a site for company "books.com". they want to maintain their existing site at www.books.com, and use a sub-domain (blog.books.com) for the new linode site.

currently, i'm using a sub-domain on a domain of mine (books.mine.com) for the development site until such time as we make the switch to blog.books.com

mail is being sent successfully from linode and received by gmail and my personal mail server, but blocked by the company's email security, so emails sent by the linode site (from site@blog.books.com) are being blocked, presumably because there is no SPF record on the domain allowing it.

my question is: what is the correct entry for spf on the books.com dns record to allow email from the dev site and ensure email from the live site is also allowed once the record is changed?

thanks again and please let me know if i'm being an idiot

v=spf1 a mx ip4:<ip.of.books.mine.com> ~all

That will do it, in parts it means
v=spf1 (spf version 1)
a (means the A record can send emails i.e books.com)
mx (means the MX records can send emails...ya need this)
ip4:<ip.of.books.mine.com> (means that the server with the ip address of your site can send email)
~all (means to softfail, i.e. if it's not in the list don't reject it totally)

that's great - thanks. and am i right in thinking if those changes are made to the domain's DNS record, i do not then have to edit or change anything else within the Linode DNS manager or Network configuration tab (reverse DNS maybe?)?

thanks again and sorry for being slow...

Nope that should be it since SPF is using the ip address not the host name.

SPF records don't apply to subdomains, so to affect mail sent from @blog.books.com you need to modify the SPF record for blog.books.com.

And unless there was already an existing SPF record for blog.books.com (or a wildcard), then SPF was not the problem. No SPF record always means pass for anyone who is checking.

That is incorrect. There should be an SPF record for every A record.

http://www.openspf.org/FAQ/The_demon_question
http://www.openspf.org/FAQ/One_record_for_each_domain

a ha - i think i get it. but i have no requirement (as yet) to send email as mail@blog.books.com. i just need to have the linode hosted server be able to send email as mail@books.com, for admin and alert purposes. the existing non-linode email server will continue to receive and manage the email accounts...

thanks for the education.