Email filters

What makes the best email filter? There isn’t really a single answer to that question. Different people and different organizations have different tolerances for how false positives versus false negatives. For instance, we’re quite sensitive to false positives here, so we run extremely conservative filtering and don’t block very much at the MTA level. Other people I know are very sensitive to false negatives and run more aggressive filtering and block quite a bit of mail at the MTA level.
For the major ISPs, the people who plan, approve, design and monitor the filters usually want to maximize customer happiness. They want to deliver as much real mail as possible while blocking as much bad mail. Blocking real mail and letting through bad mail both result in unhappy customers and increase the ISP’s costs, either through customer churn or through support calls. And this is a process, filters are not static. ISPs roll out new filters all the time, sometimes they are an improvement and sometimes they’re not. When they’re not, they’re pulled out of production. This works both for positive filters like Return Path and negative filters like blocklists.
Then there is mail filtering that doesn’t have to do with spam. Business filters, for instance, often block non-business mail. Permission of the recipient often isn’t even a factor. Companies don’t often go out of their way to block personal mail, but if personal mail gets blocked (say the vacation plane ticket or the amazon receipt) they don’t often unblock it. But when you think about why a business provides email, it makes perfect sense. The business provides email to further its own business goals. Some personal usage is usually OK, but if someone notices and blocks personal email then it’s unlikely the business will unblock it, even if the employee opted in.
In the case of email filters, the free market does work. Different ISPs filter mail differently. Some people love Gmail’s filters. Other people think Hotmail has the best filtering. There are different standards for filtering, and that makes email stronger and more robust. Consumers have choices in their mail provider and spamfiltering.

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Why do ISPs do that?

One of the most common things I hear is “but why does the ISP do it that way?” The generic answer for that question is: because it works for them and meets their needs. Anyone designing a mail system has to implement some sort of spam filtering and will have to accept the potential for lost mail. Even the those recipients who runs no software filtering may lose mail. Their spamfilter is the delete key and sometimes they’ll delete a real mail.
Every mailserver admin, whether managing a MTA for a corporation, an ISP or themselves inevitably looks at the question of false positives and false negatives. Some are more sensitive to false negatives and would rather block real mail than have to wade through a mailbox full of spam. Others are more sensitive to false positives and would rather deal with unfiltered spam than risk losing mail.
At the ISPs, many of these decisions aren’t made by one person, but the decisions are driven by the business philosophy, requirements and technology. The different consumer ISPs have different philosophies and these show in their spamfiltering.
Gmail, for instance, has a lot of faith in their ability to sort, classify and rank text. This is, after all, what Google does. Therefore, they accept most of the email delivered to Gmail users and then sort after the fact. This fits their technology, their available resources and their business philosophy. They leave as much filtering at the enduser level as they can.
Yahoo, on the other hand, chooses to filter mail at the MTA. While their spamfoldering algorithms are good, they don’t want to waste CPU and filtering effort on mail that they think may be spam. So, they choose to block heavily at the edge, going so far as to rate limit senders that they don’t know about the mail. Endusers are protected from malicious mail and senders have the ability to retry mail until it is accepted.
The same types of entries could be written about Hotmail or AOL. They could even be written about the various spam filter vendors and blocklists. Every company has their own way of doing things and their way reflects their underlying business philosophy.

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Blocking of ESPs

There’s been quite a bit of discussion on my post about upcoming changes that ESPs will be facing in the future. One thing some people read into the post is the idea that ISPs will be blocking ESPs wholesale without any regard for the quality of the mail from that company.
The idea that ESPs are at risk for blocking simply because they are ESPs has been floating around the industry based on comments by an employee at a spam filter vendor at a recent industry conference.
I talked to the company to get some clarification on what that spam filtering company is doing and hopefully to calm some of the concerns that people have.
First off, and probably most important, is that the spam filtering company in question primarily targets their service to enterprises. Filtering is an important part of this service, but it also handles email archiving, URL filtering and employee monitoring. The target market for the company is very different than the ISP market.
The ISPs are not talking about blocking indiscriminately, they are talking about blocking based on bad behavior.
Secondly, this option was driven by customer request. The customers of the spam filtering appliance were complaining about “legitimate” mail from various ESPs. Despite being reasonable targeted the mail was unrequested by the recipient. While ESPs use FBLs and other sources of complaints to clean complainers off rented or epended lists at ISPs, the option is not available for mail sent to corporations. Enterprises don’t, nor should they have to, create and support FBLs. Nor should employees be expected to unsubscribe from mail they never requested.
This option is the direct result of ESPs allowing customers to send spam.
Thirdly, this option is offered to those customers who ask for it. It is not done automatically for everyone. The option is also configurable down to the end user.
While I haven’t seen the options, nor which ESPs are affected, I expect that the ones on the list are the ones that the filtering vendor receives complaints about. If you are not allowing your customers to send spam, and are stopping them from buying lists or epending, then you probably have not come to the attention of the filtering company and are not on the list of ESPs to block.

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We're gonna party like it's 1996!

Over on deliverability.com Dela Quist has a long blog post up talking about how changes to Hotmail and Gmail’s priority inbox are a class action suit waiting to happen.
All I can say is that it’s all been tried before. Cyberpromotions v. AOL started the ball rolling when they tried to use the First Amendment to force AOL to accept their unsolicited email. The courts said No.
Time goes on and things change. No one argues Sanford wasn’t spamming, he even admitted as much in his court documents. He was attempting to force AOL to accept his unsolicited commercial email for their users. Dela’s arguments center around solicited mail, though.
Do I really think that minor difference in terminology going to change things?
No.
First off “solicited” has a very squishy meaning when looking at any company, particularly large national brands. “We bought a list” and “This person made a purchase from us” are more common than any email marketer wants to admit to. Buying, selling and assuming permission are par for the course in the “legitimate” email marketing world. Just because the marketer tells me that I solicited their email does not actually mean I solicited their email.
Secondly, email marketers don’t get to dictate what recipients do and do not want. Do ISPs occasionally make boneheaded filtering decisions? I’d be a fool to say no. But more often than not when an ISP blocks your mail or filters it into the bulk folder they are doing it because the recipients don’t want that mail and don’t care that it’s in the bulk folder. Sorry, much of the incredibly important marketing mail isn’t actually that important to the recipient.
Dela mentions things like bank statements and bills. Does he really think that recipients are too stupid to add the from address to their address books? Or create specific filters so they can get the mail they want? People do this regularly and if they really want mail they have the tools, provided by the ISP, to make the mail they want get to where they want it.
Finally, there is this little law that protects ISPs. 47 USC 230 states:

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