Who are mimecast?

Mimecast is a filter primarily used by businesses. They’re fairly widely used. In some of the data analysis I’ve done for clients, they’re a top 10 or top 20 filter.
Earlier today someone asked on Facebook if mimecast may be blocking emails based on the TLD. The short answer is it’s unlikely. I’ve not seen huge issues with them blocking based on TLD of the domain. They’re generally more selective than that.

The good news is mimecast is really pretty good about giving you explanations for why they’re blocking. They’ll even tell you if it’s mimecast related or if it’s a specific user / user-company block.
Some example rejection messages from a recent dive into some bounce logs.

  • Administrative prohibition – envelope blocked – https://community.mimecast.com/docs/DOC-1369#
  • Email rejected due to security policies – https://community.mimecast.com/docs/DOC-1369#
  • Envelope blocked – User Entry – https://community.mimecast.com/docs/DOC-1369#550
  • Invalid Recipient – https://community.mimecast.com/docs/DOC-1369#
  • Message expired -> Open relay not allowed – https://community.mimecast.com/docs/DOC-1369#451
  • Rejected by header based Blocked Senders: address@example.com – https://community.mimecast.com/docs/DOC-1369#
  • Rejected by header based manually Blocked Senders: address@example.com – https://community.mimecast.com/docs/DOC-1369#
  • Remote server returned message denied by administrative policy -> Administrative prohibition – envelope blocked – https://community.mimecast.com/docs/DOC-1369#550
  • spamcop.mimecast.org Blocked – see http://www.spamcop.net/bl.shtml?10.10.10.10. – https://community.mimecast.com/docs/DOC-1369#550

If you look at the page linked to you can see that there is a huge amount of flexibility in how and who can block mail using mimecast. Mimecast itself can push filters, local administrators can filter mail for the particular domain they manage, and individual users can set up filters. And, users seem to take advantage of that.
Dealing with a mimecast block involves figuring out who is responsible for the block. Luckily, the mimecast rejection messages and documentation give clues as to whether it’s the local administrator configuring the policy or if it’s the end user. In most cases it’s not actually mimecast blocking the mail.
Mimecast provides tools and an interface to manage incoming mail, but does not actually push out rules like many of the other appliances. That’s good and that’s bad. It’s good because you don’t have a 3rd party making delivery rules for different businesses. It’s bad because once a company administrator gets to the point of blocking specific mail it’s going to be very difficult to convince them to lift that block.
Why? Remember the discussion about productive mail?
Productive Mail: Mail that furthers a business’ goals and supports their underlying business model. Mail can be both solicited and wanted by specific endusers. But, a particular company can decide to block mail simply because they don’t see the mail as beneficial to the overall business. Thus the mail is blocked for being unproductive.
We can assume that employees who have access to create mail blocks in mimecast, and other business filters, have the authority to do so. Which means when you’re looking to get unblocked through mimecast, you’re likely having to convince the very person who blocked you to unblock you.
These types of blocks are distinctly different than negotiating with a consumer ISP or even a filtering company. There is no appealing to engagement or appealing to solicited. The business doesn’t really care about either, all they care about is their employees are working while they’re at work and using corporate resources.

Back to the office!
The inbox is a moving target

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Permission and B2B spam

Two of the very first posts I wrote on the blog were about permission (part 1, part 2). Re-reading those posts is interesting. Experience has taught me that recipients are much more forgiving of implicit opt-in than that post implies.
The chance in recipient expectations doesn’t mean, however, that permission isn’t important or required. In fact, The Verge reported on a chatbot that will waste the time of spammers. Users who are fed up with spam can forward their message to Re:Scam and bots will answer the mail.
I cannot tell you how tempted I am to forward all those “Hey, just give me 10 minutes of your time…” emails I get from B2B spammers. I know, those are actually bots, but there is lovely symmetry in bots bothering one another and leaving us humans out of it.

Speaking of those annoying emails, I tweeted about one (with horrible English…) last week. I tagged the company in question and they asked for an example. After I sent it, they did nothing, and I continued to get mail. Because of course I did.
These types of messages are exactly why permission is so critical for controlling spam. Way more companies can buy my email address and add me to their spam automation software than I can opt-out of in any reasonable time frame. My inbox, particularly my business inbox, is where I do business. It’s where I talk with clients, potential clients, customers and, yes, even vendors. But every unsolicited email wastes my time.
It’s not even that the mail is simply unwanted. I get mail I don’t want regularly. Collecting white papers for my library, RSVPing to events, joining webinars all result in me getting added to companies’ mailing lists. That’s fair, I gave them an email address I’ll unsubscribe.
The B2B companies who buy my address are different. They’re spamming and they understand that. The vendors who sell the automation filters tell their customers how to avoid spam filters. Spammers are told to use different domains for the unsolicited mail and their opt-in mail to avoid blocking. The software plugs into Google and G Suite account because very few companies will block Google IPs.
I’ve had many of these companies attempt to pay me to fix their delivery problems. But, in this case there’s nothing to fix. Yes, your mail is being blocked. No, I can’t help. There is nothing I can say to a filtering company or ISP or company to make them list that block. The mail is unwanted and it’s unsolicited.
The way to get mail unblocked is to demonstrate the mail is wanted. If you can’t do that, well, the filters are working as intended.
 

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AHBL Wildcards the Internet

AHBL (Abusive Host Blocking List) is a DNSBL (Domain Name Service Blacklist) that has been available since 2003 and is used by administrators to crowd-source spam sources, open proxies, and open relays.  By collecting the data into a single list, an email system can check this blacklist to determine if a message should be accepted or rejected. AHBL is managed by The Summit Open Source Development Group and they have decided after 11 years they no longer wish to maintain the blacklist.
A DNSBL works like this, a mail server checks the sender’s IP address of every inbound email against a blacklist and the blacklist responses with either, yes that IP address is on the blacklist or no I did not find that IP address on the list.  If an IP address is found on the list, the email administrator, based on the policies setup on their server, can take a number of actions such as rejecting the message, quarantining the message, or increasing the spam score of the email.
The administrators of AHBL have chosen to list the world as their shutdown strategy. The DNSBL now answers ‘yes’ to every query. The theory behind this strategy is that users of the list will discover that their mail is all being blocked and stop querying the list causing this. In principle, this should work. But in practice it really does not because many people querying lists are not doing it as part of a pass/fail delivery system. Many lists are queried as part of a scoring system.
Maintaining a DNSBL is a lot of work and after years of providing a valuable service, you are thanked with the difficulties with decommissioning the list.  Popular DNSBLs like the AHBL list are used by thousands of administrators and it is a tough task to get them to all stop using the list.  RFC6471 has a number of recommendations such as increasing the delay in how long it takes to respond to a query but this does not stop people from using the list.  You could change the page responding to the site to advise people the list is no longer valid, but unlike when you surf the web and come across a 404 page, a computer does not mind checking the same 404 page over and over.
Many mailservers, particularly those only serving a small number of users, are running spam filters in fire-and-forget mode, unmaintained, unmonitored, and seldom upgraded until the hardware they are running on dies and is replaced. Unless they do proper liveness detection on the blacklists they are using (and they basically never do) they will keep querying a list forever, unless it breaks something so spectacularly that the admin notices it.
So spread the word,

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Content, trigger words and subject lines

There’s been quite a bit of traffic on twitter this afternoon about a recent blog post by Hubspot identifying trigger words senders should avoid in an email subject line. A number of email experts are assuring the world that content doesn’t matter and are arguing on twitter and in the post comments that no one will block an email because those words are in the subject line.
As usually, I think everyone else is a little bit right and a little bit wrong.
The words and phrases posted by Hubspot are pulled out of the Spamassassin rule set. Using those words or exact phrases will cause a spam score to go up, sometimes by a little (0.5 points) and sometimes by a lot (3+ points). Most spamassassin installations consider anything with more than 5 points to be spam so a 3 point score for a subject line may cause mail to be filtered.
The folks who are outraged at the blog post, though, don’t seem to have read the article very closely. Hubspot doesn’t actually say that using trigger words will get mail blocked. What they say is a lot more reasonable than that.

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