Setting up SPF Records
SPF records are used to help ensure that no one sends emails claiming to be from you when they are not (called spoofing).
The receiving mail server checks the SPF record for the domain sending the mail.
The SPF record identifies all the valid servers that can send mail for that domain.
If the mail is from a server not listed, then the mail is rejected.
If there is no SPF record for a domain, then there is no check.
To create an SPF record you must add a TXT recrod to your DNS.
In your DNS text record, the first field should be:
YourDomainName.com.
note - the trailing period is required
The value field should be:
"v=spf1 a mx ~all"
note - the quotation marks are required
So your SPF record in your DNS looks like this:
YourDomainName.com. IN TXT "v=spf1 a mx ~all"
This SPF record means that only your web server (a) and your mail (MX) server can send mail for YourDomainName.com
Get more information here
spf.pobox.com and more information on all the options here
spf.pobox.com/mechanisms.html
You can do SPF record verification, validation and testing at
this site.
A few words of caution
This will only work if ALL your mail is sent from your webhost using the same IP address as specified in youir DNS.
If you also send mail from another source (such as your ISP) you are at the mercy of the ISP to have appropriate SPF records to include in your specification,
since most ISPs use many mail servers and you have no way to know which server will send your mail.
Using either the ptr: or ip4: option MAY work depending on whether your ISP has a valid SPF record which includes the servers used to send your mail.
And if you are on shared host that sends mail from a different IP address than your domain IP address, you must specify that server in your SPF record (you could use the ip4: option to specify the IP address).