Mail Server SPF Lookup Failure

[alphabet]

We use Hostasaurus for our mail server. Yesterday we noticed our mail was slow and several known vendors were receiving bounce backs with error message:

[Could not connect: Got an unknown MAIL FROM response: 451 SPF lookup failure "#4.3.0"]

I referred the senders to this link:

http://support.dshost.com.au/knowled...s-it-mean.html

The vendors said this corrected their issue.

[ILoveHostasaurus]

Re: Mail Server SPF Lookup Failure

I believe that resolution was just a coincidence.

We had staff track down the issue on the affected servers yesterday afternoon and the problem was corrected. The affected systems were a subset of our servers where, at some point in the past, one or more customers on the affected servers had used a now-defunct anti-spam filtering service. Servers where there had never been a customer who had used the specific company were not affected.

Filtering services cause an issue for servers that do SPF lookups because your incoming mail comes from the filtering service's servers and not the original sender's server. SPF is designed to tell you when mail claiming to be from a given domain comes from an unapproved server, which a filtering server would be. To work around this issue, when customers choose to use third party anti-spam filters, we have to modify our SPF checking routines to 'include' that provider's own SPF record. That inclusion means that mail from the actual sender, where an SPF record is present, is treated as if the filtering provider's information was part of the sender's SPF record, allowing it through rather than treating it as a forgery and blocking.

The provider in question went defunct recently and the lookup failures began to occur intermittently once their domain was turned off.

[alphabet]

Re: Mail Server SPF Lookup Failure

Hi David,
Thank you for the vigilant efforts. I'll let my vendors know.