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What They Are
SPF records are TXT dns records in a particular zone for a particular domain that dictate what servers are authorized to send out mail for the domain. They are becoming more an more mandatory as spam becomes a larger problem. They basically prevent spammers from using spoofing your domain, while allowing spam filters to give your legitimate email more weight.
Here is an example:
example.com. TXT "v=spf1 mx a -all"
This says that only example.com and the MX server for example.com are allowed to send emails for example.com. This can greatly reduce spam that is spoofed on your domain.
How To Make Them
99% of all servers can use the example record:
"v=spf1 mx a -all"
If you have a special circumstance where you have an in-house exchange server, or multiple mail servers, or a special mail service, you will have to make a special record.
Here is another example, where there is a second ip (1.1.1.1) that is used to send mail for this domain too:
"v=spf1 mx a ip4:1.1.1.1 -all"
If you have a more complicated setup you should probably use the openspf wizard to make sure you cover all of your bases:
- http://www.openspf.org/: Sender Policy Framwork site
How to Add Them
You need to put them in your DNS zone file, usually they are put right below the MX record. If you are using Cpanel, click on "Edit DNS zone", then click the zone you are adding the Record for, then add it like this:
example.com. TXT "v=spf1 mx a -all"
How to Verify They Work
Once you have created them you can validate that a site has a working SPF record using a site like http://www.kitterman.com/spf/validate.html
Or even just to a #host -t txt mydomain.com
Adding SPF Records to Existing Cpanel Accounts
What if you have 200+ existing Cpanel accounts. Do you have to manually edit each zone file to add the SPF record? While that does sound fun, there is a better way:
http://www.cpanelconfig.com/how-to/install-spf-records-on-a-cpanel-server/
Which tells you about a magic script that can help you out, you can find that script at /usr/local/cpanel/bin/spf_installer on your Cpanel box.
