jay-spf at kajayr
Mar 20, 2008, 2:13 PM
Post #3 of 3
(941 views)
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On Thu, 2008-03-20 at 13:19 -0700, Carlisle Winery wrote:
> I'd like to setup an SPF record to prevent our business e-mails from being
> spoofed. We send out e-mail under our domain, carlislewinery.com, via 3
> different servers - mail.carlislewinery.com, smtp.sbcglobal.net, and
> mail.sonic.net. I'm a little unclear on how to specify the latter two in
> the record. Do I use mx: or a:? In other words, is it
>
> "v=spf1 a mx mx:smtp.sbcglobal.net mx:mail.sonic.net ~all"
>
> or is it
>
> "v=spf1 a mx a:sbcglobal.net a:sonic.net ~all"
>
> or is it something else?
>
> Thanks in advance.
>
> Mike Officer
>
>From what you have defined, the simplest for you would be:
"v=spf1 a a:smtp.sbcglobal.net a:mail.sonic.net ~all"
which is similar to your first (above) without the redundant mx (which
would cause two unnecessary dns lookups by servers receiving mail from
you).
As a rule, use the method which causes least number of lookups. "a"
causes one lookup, "mx" in this case causes two lookups. As the "a" and
"mx" ultimately resolve to the same IP, there would be two redundant
lookups for mail sent out via the other two servers.
Your second would not achieve what you want as sonic.net resolves to a
different IP from mail.sonic.net
Cheers
KAJAYR
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