ORF 5.4 Sneak Peek, Part 1

The first public preview of ORF 5.4 is just around the corner and we are kicking off this blog article series to introduce you to some of the changes shipping in the new version. This first post is about the SPF update.

ORF was among the first products to add support for authenticating emails using the Sender Policy Framework (SPF) in September 2005. You can tell we got a bit early in the game, because RFC4408 — the standard that governs SPF — was published only 8 months later in April 2006. Changes between the implemented draft version and final RFC did not call for a change, though. The first update that really changed a few things is RFC7208, published last year.

We are now shipping ORF 5.4 with a fully RFC7208-compliant SPF client that can do validation as per the latest standard version. Our updated library debuted in our SPF validation services in May and has been tested by thousands of users worldwide since.

The changes introduced by RFC7208 are non-breaking, so policies published using the earlier version will be readily consumed and validated by ORF. Perhaps the most significant change is with error handling, which is more clearly defined and also more lenient than in the earlier standard version. SPF evaluation for a considerable portion of policies used to end up in errors in ORF, because they referenced non-existent DNS records, which ORF used to treat as a policy error — we argued that policy publishers would not reference non-existent DNS data intentionally, so such missing reference questions the integrity of the SPF policy. Given how common this issue is, it’s no wonder that RFC7208 now defines a clear procedure for such errors, allowing at most two such references before the evaluation ends up in an error. We have mixed feelings about this change, but we do expect it will allow the evaluation of more policies in ORF.

There have been more changes, but mostly technical — gory details are available in our earlier blog post about the SPF update.

We will be back with more on ORF 5.4 soon, stay tuned.

Exchange 2016 Preview is now available

Breaking news: the first preview version of Exchange 2016 just have been published. Head to the Exchange Team Blog to learn more or download all the 1.7GB of the latest and best from the Microsoft Download Center.

As always, we are committed to provide support in ORF for the latest Exchange version as soon as possible, so as of writing this, VMs are already firing up up and work has already started on compatibility testing. ORF 5.4 will likely arrive before Exchange 2016 goes to RTM, so we will likely dedicate a minor release solely to Exchange 2016.

Reminder: Windows Server 2003 is now officially gone

In case you missed the news, Microsoft has stopped supporting Windows Server 2003 on July 14, 2015, so if you still have an ancient server hiding somewhere on your network, be sure to migrate to a newer platform. ORF has your back with support for the most recent Windows Server and Exchange versions and we are preparing for the soon-to-be-released Windows Server 11 and Exchange 2016. Don’t worry if you are a bit behind with your ORF license, just contact our Customer Service for an upgrade offer.

Exchange 2013 CU9 Health Probe woes

You probably know the Managed Availability feature of Exchange 2013, which sends periodic health probe emails to check server health. You probably never wondered, though, why these emails are omitted from the ORF logs. And you are right of course, it just works, so why bother? That is, until it doesn’t and health probes start showing up in the logs to add a headache-inducing noise every couple of minutes.

Health probes showing up in the logs (pre-CU9, detection disabled)

Health probes showing up in the logs (pre-CU9, detection disabled)

To save you from the pain, ORF detects the list of reserved Heath Mailboxes during installation and automatically ignores any email sent to a health mailbox address. This prevents these emails from getting into the logs and your sanity is preserved.

Unfortunately, this only lasts until you upgrade to the 9th Cumulative Update of Exchange 2013 (CU9), which breaks this feature and then you get this:

Health probes in the logs after CU9, without recipient information

Health probes in the logs after CU9, without recipient information

This is due to a new Transport Agent introduced by CU9 called the System Probe Drop Smtp Agent — undocumented, but apparently responsible for dropping probe emails — which does not “drop the email” in a traditional sense, but removes all email recipients instead. Alas, this method of stopping an email from getting delivered has an adverse effect, namely the email still gets passed down the pipeline, but now with the recipient information destroyed. As ORF’s health probe detection is based on the recipient address, it also renders this feature useless.

When can I expect a fix for this?

We are still evaluating the best way to deal with this. We plan to address the issue in the next regular release. As this potentially affects other third-party Transport Agent vendors as well, we are also reaching out to Microsoft to discuss this matter.

Update July 31, 2015: The upcoming beta version of ORF 5.4 will arrive with a fix for this problem.

Is there a workaround?

You can set up a filtered view in the ORF Log Viewer for the Sender field (e.g. a regex for (HealthMailbox.*@yourdomain|[email protected]\.com)$ with rule inversion).

Can’t I just change the agent priorities?

Unfortunately, no. The System Probe Drop Smtp Agent hooks the OnEndOfHeaders event, which always occurs before the OnEndOfData event hooked by ORF.

I don’t have CU9 and still get health probes in the log

You probably added a new Mailbox server after ORF was installed and you need to update the list of Health Mailboxes. Read more on this in our Knowledge Base article.

Snowshoe spam recommendations

If you have experienced a sudden rise in spam reaching end-users recently and you are located in the USA, you might be affected by snowshoe spam. This article tells you how to configure your ORF to deal with this type of spam.

How do I tell if I am affected?

Open a recent log file in the ORF Log Viewer and sort the events by the Related IP column. Scroll through the sorted list of events and look for large, continuous network blocks (e.g. a /24) with spammy email subjects. If the sender email addresses for these look like [email protected], you are affected. Otherwise, the increase in spam may be due to a technical issue and you should contact our Customer Service to investigate.

Typical example of a snowshoe campaign in the ORF Log Viewer.

Typical example of a snowshoe campaign in the ORF Log Viewer.

How do I stop this campaign?

As of writing this, the Greylisting Test of ORF can stop the campaign easily (when configured a certain way).

  • Open the Blacklists / Greylisting page in the Administration Tool.
  • Make sure the test is enabled (see “On” next to the page title).
  • Disable the “Accept delivery retries from the same /24 subnet” option
  • Disable the “Skip Greylisting if the sender explicitly passes the SPF Test” option
The recommended ORF configuration for the Greylisting Test against snowshoe spam

The recommended ORF configuration for the Greylisting Test against snowshoe spam

Greylisting is an aggressive measure that delays emails from unknown senders for 5-15 minutes. We are working on a less aggressive technology against this type of spam. Meanwhile, make sure you also have the Auto Sender Whitelist enabled and assigned to the Before Arrival or both filtering points.

Why do I have to configure ORF this way?

The campaign is run remarkably well compared to the average spam. Instead of using a network of compromised computers (botnets), the spammer abuses reputable hosting companies with a clean IP reputation for very short periods of time (2-4 hours) before it moving on the next provider. The usual heuristics, such as reverse DNS and SPF checks also check out.

We suspect that custom spamware is used for email delivery which Greylisting fends of well. However, as emails arrive from a continuous range of IPs and SPF is properly set up for the spamming domains, Greylisting defaults needs to be adjusted for this campaign.