On 10/4/10 12:47 PM, Greg Whynott wrote:
A partner had a security audit done on their site. The report said they were
at risk of a DoS due to the fact they didn't have a SPF record.
I commented to his team that the SPF idea has yet to see anything near mass
deployment and of the millions of emails leaving our environment yearly, I
doubt any of them have ever been dropped due to us not having an SPF record in
our DNS. When a client's email doesn't arrive somewhere, we will hear about
it quickly, and its investigated/reported upon. I'm not opposed to
putting one in our DNS, and probably will now - for completeness/best practice
sake..
how many of you are using SPF records? Do you have an opinion on their use/non
use of?
It is ironic to see recommendations requiring use of SPF due to DoS
concerns. SPF is a macro language expanded by recipients that may
combine cached DNS information with MailFrom local-parts to synthesize
>100 DNS transactions targeting any arbitrary domain unrelated to those
seen within any email message. A free >300x DDoS attack while spamming.
SPF permits the use of 10 mechanisms that then require targets to be
resolved which introduces a 10x multiplier. The record could end with
"+all", where in the end, any message would pass. Since SPF based
attacks are unlikely to target email providers, it seems few
recommending SPF consider that resolving these records containing active
content might also be a problem.
-Doug